So, I discovered yesterday that the epic engineering helmets have no level requirement, just the 350 skill to use. Also discovered that you can zone into heroic Blood Furnace at 63. The result...
http://armory.worldofwarcraft.com/ch...otem&n=Bubblun
Regarding heroics, I would theorize that the minimum level to zone in is the same as the normal mode of the dungeon. With the change to getting heroic keys at honored, I'd imagine you could do this at 58 or 59.
/edited to fix the link