have a 97 4.6 cobra. want to get some serious hp.The dilemma; should I GET A new motor like from a 03 cobra or get motor work done ,like heads etc (d.s.s.) im looking for around 500-550 hp area. I know s/c can get up to 450 rwhp but not enough plus not sure motor will hold (91K MI.)also cost effective and reliability a must.