Actually an afterthought on the scrap iron ... instead of messing with smelter yield it would be better to just reduce the weight of a single piece of scrap iron from 10lb to no more than about 1.5lb. If you're going mining for metal ores, you'd better expect to be hauling ore by the ton back to your smelter ... but there's no way you're hauling a ton of scrap iron out of a single tomb unless it's a tomb complex like the Valley of the Kings. Pulling maybe a hundred pounds of scrap iron out of a tomb suddenly requires a whole lot less willing suspension of disbelief, and maintains the easy "one 'ore' item yields one ingot from the smelter".