bigger engine?

[unreconstructed1]

how are ya'll doing? I just bought a 67 GMC that needs ALOT of work. over the next few months I'll be repairing the entire bottom edge of the cab and bed alot of surface rust and a few more problems. my question is, my truck has a straight 6 in it with a 3 on the tree. what kind of work will be involved in putting a 350 in it? i figured ill have to relocate the motor mounts back toward the firewall some, but am i gonna have to change the front end? the current crossframe looks too narrow to be able to move the motor mounts back far enough to put a 350 in. just wondering