im having someone drop in a 350 in my elco he called me today and said he had a 4 bolt main off a truck (didnt say what year or model truck it came off) and said it did not fit cause the frame is only made to take 6cyl or 305 motors BUT it was gonna be possible to do with custom mounting brackets for the motor and getting a short tail transmission because the 350 trans i have now is to long he was gonna have to get a short tail transmission. I thought it was gonna be a direct swap without any mods needed what kind of problems can he be coming across