Here's what I'm thinking of getting. 1980 GMC C3500 with a 350 and 4 speed (granny low) trans. The trans. is in bad shape and since this will be a company truck (construction), I'd like to swap in a Turbo 400. Anyone know if the transmission crossmembers are the same? I'm not up on manual transmissions, what is the model # of the present unit in this truck? Thanks, Eric M.