73 340 motor worth

price sounds about right. pistons shouldn't be a problem as far as balance. Just to be safe I would tear it down and go threw it. I never trust an engine I didn't build, or know who built it. Check the bearing's to verify they are new and atleast plastigage the crank and re-assemble it. That's just my opinion, but I sleep better at night when I know for sure what's going on in my motor.