New QP 9 install
 

Just some thoughts on the quick performance 9 differential that I installed in my 68 GTO . It’s a really nice unit and great place to deal with. It shipped in 3 separate boxes - housing, center section and axles . I reused my stock drum brakes . You will almost certainly need a longer drive shaft - about 1.5” in my case and if you’ll want adjustable upper control arms as your pinion angle most likely change . Mine started out about 4.5 degrees down . I measured my drive line angles with a digital finder and confirmed things with the tremec app to dial it in . I followed their break in procedure and today put about 120 miles on it and the diff is dead quiet . I went with a 3.50 gear down from the 3.90 I had in the bop and it was a good choice. I really didn’t notice any loss of performance and feel like I have more use of the engines power band and use of each gear . I also installed a QA1 I” bar that goes around the back of the housing and it made a noticeable difference in oversteer from the 7/8 bar . It’s an economical swap but keep in mind the added coin for control arms and drive shaft .

X2 on QP, great price, quality, and customer service. My stock driveshaft fit and I ran it until I did an engine upgrade. I'm assuming you already had boxed lower control arms? My pinion angle was good and I'm still running stock upper arms. Can you post a Pic of the sway bar?

I've installed them in others cars and currently have 2 of them in our personal cars. They fit and perform as expected. Pinion angles good right out of the box. I've never had any issues with them.

Do they center the pinion with the center of the driveshaft tunnel?I know the stock rear in the f bodies are always offset.

We are going to find out. I bought a Moser 9" for my 1976 Firebird, going to install it this weekend. They had a great deal on the kit this past winter, about a third off. By the time I would have updated my 8 1/2" 10 bolt, it would have cost a similar amount. I looked into C Clip eliminators and all the companies who sold them did not recommend them for street or auto cross use. Once it is in, I will have to get a driveshaft made. Upgrading to 1350 u joints. Going to use the 11" rear drum brakes I already have on my Firebird.

Strange does, or did, make a C clip eliminator for stock diameter axles that uses the 3.150 taper bearings as their "Street" C clip kit vs roller bearing kits.

Probably going to use a QP 9" in the 64 Impala project. Thinking Explorer brakes. The GM pattern ends for 3.150 make the backing plate bolts really tight