Sorry about the delay in replying. I completely missed your post.

I let a muffler shop install them for me. The stock exhaust was so rusted that I didn't want to deal with trying to remove rusted bolts, breaking bolts, etc. One of the original cats had already been removed and a pipe welded in its place. The other cat was rattling because the insides had hardened. The old muffler had a hole rusted in it too. So I had the magnaflow cats and my Hooker catback installed at the same time. So I can't say if the cats themselves helped performance. They fit pretty well, although the drivers side pipe hit the crossmember just a little bit. A small bend in the pipe fixed that.

 

Update: Headers are installed. I finally got those last few bolts started, but only because of the type of bolts I used. I got some Spectre locking bolts from AZ. They lock by inserting a wire through the head that runs from one bolt to its mate. So each bolt head has holes drilled sideways through each flat surface. I got one finger under each of those bolts (I could only get one finger at a time to touch these bolts) to steady it, then inserted a tiny allen wrench into the sideways holes in the bolt head and turned it with the allen wrench to get it started threading. Then I used a small ignition wrench to tighten it up. Cheapo AZ locking header bolts FTW!!!

I do have a leak, but I don't think it is the headers. I believe it is where the downpipe from the passenger header connects to that side of the y-pipe. I had to cut out the flex joint part of they y-pipe and connect the header down-pipe to it. I used a u-bolt muffler clamp to hold it together until I could get that joint welded. I am taking it to the muffler shop tomorrow to have that joint welded and let them do a leak test to see if I have leaks anywhere else.

I am very disappointed with the way these headers fit. I had to bfh the passenger side on one of the primary tubes to keep it from touching the plastic heater box. And I had to bfh the collector on the drivers side to get the #5 & #7 spark plugs to fit. Even if I installed the plugs first, then the header, it would not fit with those plugs in place. As a result, two tubes are pinched to about 3/4 the size they should be on the drivers side. If I get this leak fixed, I plan to go to the track this weekend and see if I gained anything. I was so impressed with my Hooker catback, but I am far from impressed with these headers so far.

Anyway, thanks for all the tips and encouragement. Sometimes it helps just to hear someone else say "Yeah, I know how you feel. Let me tell you what happened to me when I installed mine...".

 

Your post is pretty indicative of most people who have installed shorty headers. They are typically a disappointment.

Luckily you don't have emissions in Thomasville, so you should be able to swap them for longtubes once you get sick of them.