Chevy and GMC engine blocks share the same bellhousing bolt pattern, so that's not a problem. 47 was the break point between the crash box and the SM-420 transmission on most of the trucks, so it's possible you've got the later model transmission. Does your shifter have a reverse lockout trigger? If not, you've got the SM 420. You'll need to fabricate a bracket to move the front motor mount back a couple of inches and do whatever adapting the exhaust pipe and throttle linkage requires, but overall it's a pretty simple swap. Good luck!
Jerry
