[Brian Baker]

Is there an aftermarket double-hump crossmember out there for installing a TH400 in place of the TH350 in my '80 Firebird that doesn't require redrilling the mounting holes towards the rear of the subframe? I remember having to relocate the subframe in my '79 T/A about 4-6" rearward when installing the TH400 and if I can avoid redrilling holes, the better.

[Skip Fix]

Yes a Summit or G Force crossmember. Same one I think G Force makes them for Summit. I use one on the 79 Camaro/IA project.

[Brian Baker]

Thanks, Skip. I was looking at the G-Force but was unsure if it had an offset for the TH400 so the factory mounting holes could be used.

[Grand73Am]

I haven't used the Summit crossmember, but it gets great reviews for fitting. This application is for putting a th400 into a 75-81 TA, so it looks like it's made to bolt in without having to make new holes. The only thing some reviewers say is you might want to drill out the frame holes to 1/2" size, since apparently it comes with 1/2" bolts. But, that's probably not even necessary, and you could still use the original 3/8" bolts. I'll probably get one myself, since I may use a th400 in one of my 79's. You can read about it here: https://www.summitracing.com/parts/sum-770317?rrec=true

[Skip Fix]

I used 3/8 bolts on mine. I'll post some pictures tonight I took awhile back. It is about 5-7lbs heavier than the factory one. You can use the TH 350 one and cut the tab off and weld on the opposite side but if you have a deep pan on the TH400 it needs notching.

[Skip Fix]

Here are some pictures