well, for starters take caps lock off..
and i'd look at it the same way i'd look at an ls1.
so piston slap, oil leaks, oil usage, service history
all the usual used car stuff....
not sure if there was anything specific with the 300kw c4b motors
From reading on the ls1 forums, the C4Bs munched cams and valve springs I think. Sounds like they were a bit of a time bomb until the cam got swapped out.