[gordon]

The core engine would be absolutely a vanilla GMC 270 - block, head, crank, cam pistons, etc, etc, etc.

About the only major external components that can be messed with would be manifolds, carb, water pump, electrical add-ons, and of course the sump...

Sump ? yes, variety of sumps, early late, angled ( for DUKW hull clearance ) with varying capacities, different dipsticks ( no jokes please ) and stuff like that.

I do have the GMC interchange lists somewhere, showing what parts had to be swapped to make any variety of 270 into any other variety ( like conventional truck engine to cabover, or DUKW, or DUKW back to ordinary truck or the like, but it doesn't mention anything like the TA application.