have rb25 head machined to fit rb30, mild porting and bigger than usual springs - $900 take it away
may seem like a bit, but that is machined AND ported already done for you
then just sell your stocker rb25 head on forums.
also have rb30 block. from series 2 vl calais - correct block for rb30det conversion. has 160,000kms on it - clean block. 200 for block ready to go.