I agree with Carl completly.
If you are going to the expense of putting splayed caps on the block use the billet.
The "old wives tale" about the difference in material is bull.
All the aluminum block use billet & I think the expansion rate between aluminum & billet is a bit more than cast & billet
Only thing we do on the aluminum blocks is tighten the clearance up on the mains a bit.
The Oliver or ProGram caps are the ones we use.
With that said, unless you are limited by rules get a Bowtie or Dart block.
They are way thicker, the lifter bores are where they belong, blind head bolt holes, thick deck, priorty main oiling,,, the list goes on.
By the time you do a stock block right for a 700+HP deal you will have put a huge dent in the price of a Dart
You can also order it with a raised deck & cam & wide pan rails for about the same price.