What motor to go with?

The 904 does need some beefing up. If you just get a run of the mill 904 it won't last a long time behind a strong 340 if driven hard daily.

My old trans guy preferred the 727 over the 904. Said it was easier to adjust the shift hardest just were you want it. Told me it would last even longer then the many years the 904 would. In his mind the 15 extra hp with the 904 wasn't worth it.

I still got the 904 trans, his brother took over and he was more for the 904's