Tranny Recommendations for 600 HP

My 904 lives behind 524/527 and has been back and forth across Canada , will be doing it again and thats with a stock valve body , but all the good parts elsewhere including a billet steel front drum and I drive it like I stole it everywhere I go , in fact I was talking to another member about putting a manual valve body in it because I end up driving it in 2nd everywhere around town because the the speed limits keep the revs to low in 3rd.