Fairly certain your selector stop is the issue, assuming front trunnion is where it needs to be, which is hard to screw up. Are you getting bolt ride over, or just trouble getting mags in?
Selector stops are rarely a plug and play piece. That little piece of steel is your only correct way of establishing your mag fit. I usually use several surplus mags, both new and used from various countries as a guide when fitting the selector stop/trigger guard. Never would I use a Korean or US mag. Your situation is unique based on your state's laws, so I don't know what to say.
Also, don't dick with your mag catch. The only piece you should have to mess with is the selector stop, which probably means you need to remove the trigger guard from the receiver. I'm a firm believer in using small screws to temporarily attach a trigger guard assembly for function check.