One of my friends got burnt on a deal like that once. He traded a fresh 360 for a 1972 340 that had been used in a truck. Supposedly ran great and he wanted it for a Duster he had (I ended up buying the '71 Duster and '71 Demon from him, with the 340 and all the parts he gathered up, including a complete 4-speed setup for about $1,200). I Bought it knowing ahead of time that I was going to tear down the 340 and do a full rebuild regardless of condition
When I got the 340 torn down I saw the bearings and crank were annihilated, the previous-previous owner that had it in the truck had a 360 Flywheel behind a Cast Crank 340. Completely destroyed the crankshaft and wiped out the bearings. My friend was standing there, giving me a hand during the tear-down, because he was curious what it looked like inside too. (needless to say he was a bit upset)
It now has a Forged Crank and is built to '71 Specs, a spare Date Coded Ready to Drop in motor for my '72 Demon in case something happens to the numbers matching engine.