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The two bolt holes I have marked with pens are blocked when the plate sits in place. There is no way of mounting the trans to the adaptor plate using these two. It would seem sensible to try and use all mounting points.
My only option seems to be to bevel the holes and weld (or what?) the appropriate bolts in place and use nuts.
How did it turn out. I'm looking to use my th350 as well. Did you use the th350 converter or the one from the ls motor? Thanks.
I am using the old th350 converter. All was going excellent tonight. My modified pan fits great, the trans crossmember lined up perfectly, the modified bop trans adaptor plate fits, converter hub spacer fits, flexplated torqued and all. Until... the holes on the LS flexplate don't line up with the converter. I was just about to seal the whole thing and had to tear it all apart again. It was all in the car waiting for the fuel line and electrics to be connected.
One thing that complicates yanking the motor out ten times is that the sump on the Moroso 20140 oil pan is very bulky. The trans and engine does not come in or out together, unless the oil pan is removed. Unbolting the engine from trans - still in the engine bay - with the heavily modified adaptor plate is a bitch.
You can never get too naive while doing an LS swap for the first time. So, there you go: the 100 dollar LS-to-old-trans does not fit the stock th350 converter out of the box. The bolt pattern is off by maybe 5/16".
Last edited by freda155; May 16, 2016 at 04:44 PM.
How did it turn out. I'm looking to use my th350 as well. Did you use the th350 converter or the one from the ls motor? Thanks.
Study closely and you will see three beautiful notches for the bolts to the rear main seal cover. The concealed chevy bolt fits inside the BOP bellhousing. The passenger side top BOP bolt hade to be welded. The middle BOP bolts had to be countersinked and then welded. I also added the LS uniqe top bolt to the plate.
Thanks for responding. Looks like I am going to do the same thing you did. I'm picking up a motor this weekend. Please update us when it's in and working. Thanks again.
How do you mount up the torque converter? Did you have to use spacers on the bolts too?
Just bolted it right up, no bolt spacers.
Haven't had any issues with this solution over the past two summers. I even took the trans out from under the car, it actually worked with the long fixed bolts and everything (engine in stock position and hooker swap headers still in place).
do you know how thick your spacer was? Im just concerned with pulling the converter out of the trans 1/4"... cause I will be driving the car at the track some.
do you know how thick your spacer was? Im just concerned with pulling the converter out of the trans 1/4"... cause I will be driving the car at the track some.
Ive used a few of these adapters before on sbc trans swaps. They usually come with converter washers of the same thickness as the plate. Since u are moving the trans back from the engine via the new plate, the converter moves back as well.
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BOP TH350 on LS1 
