I would go aluminium big block, I helped move a R3 tall block on the weekend and it is around 235 lbs or around 100 more than a big block Aluminum block.
Saying that the guy is shooting for 1600hp with the R3.
I have asked this question a few times in some of these discussions over the yrs,. where and who still makes an aluminum r/b wedge ???????????? thinking their non existant know--extinct !