Yep so its only for the rox blocks.
283 Main ROX Series Block, Gray Iron 25534452
Still looks like a pile of money but these engines are not gm only you can buy the blocks and heads new or used. Gm does supply the racers with build up blocks about a year a head of time so they can prep for next season.
I see gm has an allout race only head for the ls engines as well. I figured these were them. But not completely different item. Rox is none catalog.