Couple of things I can confirm for you now. I did move my save and start fresh. I got up to level 25 before finally getting both backpack and helmet. The helmet dropped on the foundry on level 2 and the backpack on the oil fields of level 2 so I believe those levels are good bets for the drop. Doing any level earlier than stage 2 of normal meant I either got low level gear or higher level gear.
Also, I can confirm, the overlord achievement won't unlock on the final boss version but will on any other.