maybe you need t pull the engine and see what you got? maybe its not as bad as it sounds? maybe it'll be cheaper to fix ( rebuild ) than buying a 5.3 ok maybe a 6.0 lol!!

i do see your point but without knowing exactly the problem just hard to justify swapping 5.3 into a 6.0s spot. personally id pull the head find the problem if it is indeed a lifter, maybe you'll get lucky and it may not have killed the bore, then again it can be sleeved if not mistaken ?