I'm installing an MN12 T56 from a CTS-V into my 3rd gen. I installed an f-body extension housing and the top and bottom machined surfaces are at a significant angle. The shifter mount and trans mount appear to be affected. Has anyone else seen this?

Yes the early 4th gen and late 4th / GTO all exhibit this.

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Interesting. Now I'm less concerned, but more curious. Any idea why?

It doesn't cost more to stamp a crossmember with a 6 deg slant. And the way the stock shifter stick bolts on, it had room for the rubber isolator and it's centered to the console. Designed to a cost.

The 32 spline housings aren't like that.

How is your hybrid buildup coming along?

Not too bad. It's my first experience with a manual transmission, so it's been pretty educational. I want to do a 32 spline SSR mainshaft, but they seem to be backordered everywhere. I'll then have to have the tail housing machined for the larger bushing and get a TH400 yoke. It should be a pretty stout transmission when complete.

I read that I need to go with an LS7 slave to avoid having to use spacers and such, so I got one of those and the appropriate pilot bearing. We'll see how it goes from here.