The triangular handgaurds will fit. Keep in mind that the right and left sides of those handgaurds are slightly different (they aren't universal like the A2 style handgaurds).
You might also consider swapping the stock and pistol grip for A1 style units (the A1 stock is shorter, and the pistol grip lacks a finger groove). That would get you fairly close to the look of a later M16A1, the most obvious differences on the DPMS rifle being the PG and shell deflector (as you mentioned), the rear sight assembly (the various models of the Colt SP1, M16 and M16A1 only had a windage adjustment on the rear sight), and the reinforcing on the lower receiver near the rear takedown pin. You could also swap out the A2 flashhider for a later A1 flashider (not closed in on the bottom).
One other option for a more accurate look is to build your rifle using historically accurate, reproduction retro lower and upper receivers from No Dak Spuds. Check out Retroblackrifle.com to learn about the various models of early ARs / M16s to decide on a particular model. I'm currently working on a very early Colt 603 / XM16E1 build (pre adoption M16A1), and I'm having a blast. But be advised you can end up spending more than $800 on such a project, especially on an early model with their unique, pricier dimpled pins/levers, including tools for assembly if you don't already have them.