Crossmember info
 

My 72 C10 truck came with a floor shift welded tunnel. I'm guessing 4 speed now is a automatic column shift, Don't know if at one time it was a 3 speed on the column & 3 speed moved to floor, Tunnel doesn't a tunnel bolted. cover Just a welded plate on tunnel.

Question is, IS there a difference between a 3 or 4 & a automatic crossmember ??

Re: Crossmember info
 

Far as I know the 3/4 speed manuals didn't have a trans cross-member, just the bell housing mounts. Automatics had the cross-member, but not sure how different they were between turbo 350, turbo 400 or powerglide.

Re: Crossmember info
 

I would imagine automatics utilized the same x-member just located fore/aft as needed for the trans length requirement to keep costs in check.

3spd column shifted trans definitely didn't have a traditional x-member under the transmission. They had extra support near the bell-housing. Early smaller 4spds were prob similar (again to keep costs down) but as the standard trans got bigger the need to support them required going to the same x-member auto's would have used.