I forgot - but did you get the background info for your car from Pontiac Historical Society (PHS)?
I'm going to check on the direct swapping of an ST 300 for a TH 350 here in the archives, but I think it's a direct change.
It you have the time today (this evening for you), we could tackle the rear end info. I am just sitting around my office waiting for an electrical contractor to replace some high voltage components. It's too dang hot out there to be watching them all the time.
If I remember right, you have already pulled your rear axle. Just grab some sand paper and start sanding through the surface rust on the back side of the drivers side axle tube near where they welded on the brake pipe clamp. Should be a 2 letter code.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
