One option is the MN12 Thunderbird / Cougar / Mark VIII rear end. They have 7.5 or 8.8 gears, an optional limited slip and the later years, disc brakes. The entire cradle will drop out of the chassis as those cars are uni-body chassis.

Mark VIII's are almost the same car as a Thunderbird / Cougar but use all aluminum center section 8.8's, cast aluminum lower control arms (vs cast iron - WTF) and most have discs.

The years that have discs most of the time are 1995, 1996 and 1997.
The RPO code in the driver's door tells you what diff size and what gear ratio the car came with factory. The RPO code also tells you 7.5 or 8.8, but I can't remember which RPO codes went with them.

The axle tag will look like this:
S 5 1 0 F
3 0 8 8 8 4 L 0 2

3 08 represents the 3.08:1 gear ratio in this case.
88 denotes an 8.8 center section
while the "L" in 4L02 denotes a limited slip carrier


Limited slip rear axle ratio:
G H - 2.26
B C - 2.47
8 M - 2.73
7 - 3.07
Y Z - 3.08
4 D - 3.42
F R - 3.45
5(W5) E(XE) 3.27
6 W - 3.73
2 K - 3.55
A - 3.63
J - 3.85

 

I will add this information to my shopping list. It almost looks like I might end up with a mishmash of parts to make an assembly. My biggest hurdle is 65" total width in the rear and 62" in front.

 

That is when you pull out the welder and make your own rear control arms to the length you need...

 

This guy took the unconventional approach to your track width problem. He sliced his MGB end to end and widened it about 12" so he could stuff a Corvette suspension under it.

Link to MGB Corvette Build

 

http://v8roadsters.com/ makes a bolt in rear subframe for miatas that will take several different kinds of center sections including cts-v and ford 8.8. You might call them and check dimensions and have a plug and play solution. It will allow you to run miata upper and lower control arms and rear hubs and has plug and play axles of several different strengths. The Miata geometry is excellent and it opens up tons of suspension and brake options for the rear.

 

I already considered just splitting the entire body right down the middle. I also considered widening the front and rear fenders to give the flat sides more of a coke bottle look. I think I can narrow the rear by making my own cradle and getting shortened half shafts. My neighbor has a C5. So today I am going to take some dimensions off it. I already located a complete front and rear suspension combination with the torque tube for about what I would spend for a set of big brakes. This continues to look like the best option.
I do like the Miata thing, so not ruling out anything yet.

 

I think the c5 is going to be way too wide. I like the Miata option. From a quick search a Miata looks to be the right width for you. Keep in mind that when you start narrowing an existing design it will change the suspension geometry, which may not be so good...

BTW, the Miata and the second gen RX7 share the same mounting points for the diff. So any 8.8 IRS mounting hangers for the RX7 will fit a Miata, with the exception of the front diff mount.

I think a 8.8 diff hanger from Ronin, combined with Miata suspension in the rear would be a good option.

Andrew

 

The IRS Explorer diffs seem to get used a lot. Check out norotors.com for info on the guys swapping RX7. There are kits for both IRS and solid axle. At least One of the members there posts here and runs into the 8s so I expect you could get some good insight into what works - that car is solid axle I believe...

 

I went shopping again this week. After studying the entire suspension thing and finding Dobertin's website. I went with a hybrid of C5/GTO rear and C5 front. No, it won't be a bolt in, but nothing will be.
Now I need to make a final decision on wheels and tires. Part of my reasoning for the C5 is the ability to fit up to a 12" rear wheel and easily a 9.5 up front. Swap meet at Atlanta Dragway this morning. We will see if any thing good shows up.

 

Made a bit more progress this weekend. Wheels and tires arrived so I had them mounted. I mocked up both front and rear cradles under the car. I have decided that the existing flares were installed too high on the side of the car. One of the next projects is to break out the plasma cutter and remove them all together. The current plan is to split and widen the stock fenders and build new wheel well lips. This will give me a chance to practice with some of my new tools. I will post up some pictures when the wife moves her car.

 

Like I said in the beginning I suck at documentation.
I have been successful with some of the dirty stuff, cleaning and painting chassis and brake parts. I went ahead and bought a TR6060 from a Camaro along with the flywheel and clutch. So now I need to sell of my T56. I also ordered gauges on the Speedhut promo. Pretty much the same as I had in the GTO.
Last weekend I made the first part of the frame rail sections that will join the front and rear cradles. I will post up some pictures this weekend.

 

Awesome project! I'll be watching this! Get the pics posted to Photobucket and then copy the link and post in your comment.

We are building a 70 MG Midget with a 2.3 SVT ford turbo/T5/cut down 8.8. 325 whp and 1700 lbs.. We are doing a Mustang 2 Front from Speedway and a triangulated 4 link in the back.

 

I started down that path with this one. But sitting by yourself and plotting is a very dangerous thing. This has grown into a far bigger undertaking than I first planned. Pretty much like every other one I have ever done.
Sunday, between rain events, I rolled the engine outside and spent some quality time with bottles of simple green a scrub brush and my pressure washer. So far so good. The leaking PS fluid that covered the pan and lower block cleaned right up.

 

Six hours with a laser site, level and other tools of destruction I have the main side rails tacked together. Doesn't look like much so far.

 

Like I said, I suck at regular documentation. The engine and trans are mocked up for fit, the rear end housing is blocked in. I ran out of shielding gas so here I sit till next weekend.

 

Next weekend is building the rear end housing cradle, trans x-member and mocking the outrigger rocker rails. That should stiffen things up quite a bit.

 

Looks like things are coming along, very nice. Sucks about the shielding gas, that stuff is getting so expensive.
Clay

 

You mentioned buying a newer TR6060 Camaro style transmission. Look up the model of it and associated gear ratios. Some of them are not great for a 2500lb gear with awful 1st gear ratios and the rest of the spread not so great.

You want the 2.66 ratio trans that came in the ZL1 or CTSv:
https://en.wikipedia.org/wiki/Tremec...0_transmission

For diff choice.... the 8.8" IRS aluminum case IMO is a good call considering the abundance of gear ratios available for cheap new and also a plethora of LSD options. That size ring gear can handle anything you plan to throw at it without even blinking. The Explorer rear end with 2 front mounts is preferred... either will work though. I'm surprised you didn't go with an aluminum diff as I see the one you mocked up is a cast steel housing. Also the stock Camaro clutch/flywheel weighs a ton. I'm hoping you put in an aluminum flywheel!

 

very cool project!