I found a 390 in the back of my garage that i never knew i had. I pulled it apart and found a couple of issues.
On one piston the one snap ring was broken in half. Never found the other half but the snap ring groove is fairly chewed up, the rod bushing is worn away to nothing on one edge, fairly evenly all the way around and the still intact end of the bushing hangs out past the rod. The piston looks fine, no scrapes on that cylinder either.
What could cause that?
The other issue is the crank end thrust is almost 1/4". Crank has such a deep groove in the back of the journal you could almost fit another thrust bearing in place. I would guess a torque convertor not into the second set of splines. The engine appears to be very low miles, D4TE block and standard bore and bearing sizes with hardly any wear, very clean inside too. No obvious grit from that worn crank thrust surface.