this is my first project.. so bare wit me.. im looking at a ls1, lt1, 350, nd 383 engines to put in my 84 regal. i was looking for power plus good mpg.. it already has a 3.8L v6 dat only has 57,00 miless on it.. no rust no dents no nothing.. jus that motor dat issnt really ever been broking in.. if i put a flowmaster kit on it wuld that give enough power to push 24" inch rims.. and still have good mpg or wulld it b better to jus go wit a whole new motor.. ls1, lt1, 350, 383 stroker????/