Rennlist is the best 944 source available. Pelican is a waste of time and 6speed doesnt cover 944’s (to cheap). Dont bother modding an NA, it’s a complete waste of time. Swapping a turbo engine in isnt worth your money. The only options you have, leave it stock, swap a 968 engine in (I know of one, race prepped, incredibly strong for $4500 ready to drop in) or swap an LS1 (your best choice). As for the head, get a used one for a couple hundred bucks and slap it on.