I just weighed bbc iron head at 63 lbs and 392 head at 69 lbs---I'm pretty sure hemi 392 block is lighter than the bbc altho I can't find my notes on block weights--crankshafts pretty much with 2 or 3 lbs and if your talking 454 bbc the dampner/flywheel are much heavier---rods will be within a few ozs, hemi pistons are a little beefy because of the top for the hemi head but the bbc is heavier by a few grams as it has a big dome also. You can put aluminum manifolds on any of them , dist and oil pumps will pretty much be a trade off and the hemi rocker shaft assy will be heavier than the individual stamped rockers ----