There is the small plastic stopper on the right side of the black drum, there is the chip you need to swap, and then there is a change in the front left area near the drum. See the attached image. At one point you could remove the pieces and just swap between the 2 drums, but apparently they modified it making it impossible to do that now.
Some people have said that this piece is a spacer to keep the drum a certain distance from the development unit. I say it's not. I've looked at it pretty closely, and as far as I can tell, this piece does not touch the development unit at all. What I've started doing is just clipping the tab off with a small pair of end cutters (nippers), down just far enough so that the drum fits into the machine. So far haven't had a bit of problem, which if that truly was a spacer, I'd figure I would have seen one by now. Just my opinion, your welcome to try if you like, or not...
Konica-Minolta DR-313 Drum Comparison.jpg
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