A small block Mopar 273-340 "A" V8 weighs 525 lbs.
I would say it's safe to say that the crankshaft will weigh in at 70 lbs.
The camshaft at 20 lbs.
Rods and pistons will weigh in at 10 lbs per ea. assembly.
Remember these are guesstimates but they're probably pretty close.
So the estimate comes in at 355 lbs. And that sounds about right for a bare block plus heads. Give or take 20 lbs.