someotherguy
+1y
Just by looking at it, not going to be easy. If it were a Vortec engine the difference between the 7.4 and 8.1 is pretty obvious as long as they're in light duty trucks, the 8.1 has coil-near-plug and the 7.4 has a traditional distributor. (late Vortec 7.4's used in medium duty were also coil-near-plug, increasing confusion)
I'd expect the guy to have all the supporting receipts for parts, machine work, whatever - or just assume it's a generic big block.
Good luck!
Richard