Back in his glorious prime, when he was on the proper gear, Pacquaio was a mini monster. Each time he was written off as having bitten off more than he can chew he stunned the boxing world by conquering bigger and bigger foes. However I think a full blooded 160 pounder would prove a bridge too far, particularly a middleweight of LaMotta's class.
La motta by brutal beating, lamotta either stops him to the body or wins a decision. He was not a KO artist but he was very strong and threw alot of punches. With this style matchup the size would really matter alot
Pac was 144 in the fight, though lol If LaMotta is nice and comes at the MW limit, he would still have 16 pounds on him at the least.