I talked to Ken at Indy about a smaller cubic inch build not too long ago (528"). He said with the "as cast" head, you could probably get away with it. He told me they had experimented in the past with a smaller inch Predator, and found they had to turn it high rpm to make power. He said you could do it, but the engine would require a lot of valve spring maintenance.

There is/was a member here that had a 480-ish" Predator build, but I think they were running nitrous on it.