Your long term goals point to the RB block. So if that is your plan, go RB. The other option is an Indy Max low deck aluminum block.

But IMO, a 511 CID low deck (4.25" stroke x 4.375" bore) will make the power goal. Aluminum main caps (can be made to 440 main size like mine is), and some block filler will minimize risk if the cylinder walls are thick enough. I had to sonic check a few blocks to be happy, and I am just over 700 hp (not B1 heads).

1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1