I used a Direct Sheet Metal for my '31 with a C4. I suspect that you might have to call them for that size transmission though - also to match your firewall. I still had a fair amount of rework to fit the recessed Brookville firewall Direct Sheet Metal Catalog/Price List.

Also Bitchn' has some real decent firewalls and floor parts.

Then, of course, you can roll a piece of 16-20 ga cold roll around some large diameter pipe, barrel, cut at an angle, add some flanges and you have the same for lots less money