Unless its a 2000+hp engine, then I wouldn't bother. I know most pro-stock guys run Nodular caps. I had a Sonny's/AR 5 inch bore space Pro-Stock block in the shop last fall, aluminumn block, guess what kind of caps it had? Nodular. This was an 804 inch engine, that made somewhere in the neighborhood of 1700hp. Another thing to consider, is all diesel blocks use nodular caps. They support sometimes 25:1 compression with 40psi of turbo boost, at 2000rpm. Talk about hard on mains.
Frank