i had to sink my clutch shit into my fire wall alot, and that was only for 18's but with a 6 5/8 body drop as far as th booster, cavi ones work good and reces it int the fire wall but dont move that clutch rod on to much angle cause you will put evil stress and blow the line, this from experience, but ive never seen a box body lay on 20s with no tubs in the firewall, unless you cut off the fire wall! ha, anyway good luck with your ball joints too, youll be cutting those and notching the lowers tom clear them 20 rollers.