401's will run hotter than 360's just like 400 chevy's run hotter than a 350. it's the thin cylinder walls. that said you shouldn't have problems unless you're towing.
Fuel and timing will effect engine temps some but they effect EGT's mainly. if your problem is as severe as it sounds it's cooling system related.
Is it blowing water out ? just wondering about a compression leak.
I still suspect the radiator. seldom have I seen a cooling problem that a radiator didn't cure.