1st gen in 66

[DSeamans]

My friend is buying my father-in-laws old 66 power wagon and is wanting to put a 1st gen cummins/tranny in it. We looked at one today that was trashed - dead miss, extreme white smoke and you could smell the fuel in it, metal on the dipstick. The truck had been rolled and he still wanted $2000. That was an obvious no. Are there specific things to look for on the early ones that aren't so obvious.

Thanks for any ideas,
Dave