A bigger deal than missing logbooks would be how it was overhauled. It's perfectly legal to overhaul an engine to 'service limits'. That *could* mean opening it up, and if everything measures within limits, simply reassembling it, replacing only things that are specifically single use, like the rod bolts. So you could be buying an 'overhauled engine' with 1500 hours already on it. I paid that price when I had a set of cylinders 'overhauled'. I knew better, but forgot to spec 'new limits'.
Regardless, buying *any* a/c engine is rolling the dice...
Charlie