If this is added then we would have to make it fair, so overload would have it's own (E) drop zone with the highest (E) items. I doubt anyone would try to do overload for some (E) parts. And doing lower levels would mean lower level (E) parts.
Also, as Tricky said, only lvls ~221 would bother doing maps over 64, since they're pretty hard after getting to tier 2 zone.
And as the drop rates would be even lower than T3, I'm pretty sure you'd die as a lvl 221 on lvl 64 before getting one, or you'd run out of time.