55-59 chevy and gmc trucks came factory with v8 motors, while there are some differences in gmc and chevy frames
the cabs are the same, a sbc and th350 will fit without any floor or firewall modifications
the crank pulley should be very close to the x-member, i suspect your motor is too high
post a pic
truk came with a 350/350 that was poorly installed on the original front motor mounts
with the sheet metal on the truck i was able to fab up these side mounts
