With headers, decent exhaust and non emissions concerned tuning it will easily be over 500 HP without removing the valve covers, how much you looking to make?

As for the trans, their tranny to work with 500HP is $2200 plus the stuff to adapt it but a 545RFE bolts up and can be had for a few hundred bucks, even some mods to handle more power are not much, kinda wondering why the bother of the 2004r? Heck an A-500 is a bolt up and cheaper to handle a lot of power... mine is holding up fine with 550lbs TQ and can be duplicated for a lot less than those trannys.