I have a th350 in my gn. We have a tranny builder in our chicago land buick chapter(trans pro ) out of lansing IL. His th350's are good for high 9's and anything faster he recomends a 400. As far as crossmember i just went to the bone yard and bought a crossmember from a 3 speed g-body car, malibu, cutlass , monte carlo, or regal. No driveshaft mods either. w/ a 400 you change the yolk and possibly shorten the shaft. I have a 3200 coan conv. for 595.00 they have a grand national as a test mule plus the trans builder is a jobber for coan so he gives you a little discount. I think the trans , converter, and t-brake was around 15-16 hundred dollars. Im happy. :smile:
ps. if you call Coan ask for Walker.