6.2's are NA engines and 6.5 are the turbos. I don't know if there was a 6.5 NA engine or not.. I have not seen any here.. but that does not mean a lot. I'm sure someone will chime in with more info.
Lots of NA 6.5's out there in HMMWV's. AM General makes brand news ones right now for the rebuild programs.
The sure way to tell is block casting numbers-these are 6.5's:
10149599 (92-93 blocks.could be 6.2 or 6.5),
12552929,
10237141,
12555506
A 506 cast by Navistar is the best, it will have "506" in raised dots in the galley under the intake and the cast Navistar Diamond logo.
Generally if it has a serpentine belt drive it is a 6.5, but that is not a sure thing.