Part 4 so here you can see the problems after the fact. My department will not allow me to alter the weapon at all so I can not mill /lathe the upper. Even without a baseplate the Deltapoint Pro is too high and covers the rear sites so no OEM cowitness.
Rather than mill the slide which you are not allowed to do, have you looked at milling the sight slightly? From the pictures it looks like only a very little amount would need to come off the front.
I'm about to have to deal with this same problem.