http://performanceforums.com/forums/...-cylinder-head Ported head shouldn't really slow spool if done right.

I seen a .86 3071 crack 507hp from a 2.4 (and not a K24) but that was a dynapack and it had a blown head gasket at the time. So 3076 on a 2.5 should be capable of at least that but de-rate that number for whatever dyno you're using and again for pump fuel.

More relevant: I've seen an RB25 do 400hp on a dyno dynamics dyno. 1jz should be able to match that and beat it with cams.