TM 9-1005-249-34 says to install the roll pin with a 1/8" punch.
The roll pin fits tightly in the receiver but loosely through the hole in the trigger guard, so the guard will hinge down.
There is NO FRONT PIN in the GI guns or those made to GI dimensions. The trigger guard (assembly) has a spring loaded detent built in to serve as a latch
The trigger guard swings down to allow clearance of the winter trigger kit, which extends the trigger down the front of the pistol grip for use with mittens.
At least a few of the "arctic triggers" were made, I've seen pictures, but they were never issued or used, in any quantity, simply because some bright fellow(s) discovered that they weren't needed, with the guard swung down you can get your mittened paw on the trigger just fine.....AND....the Army issues trigger finger mittens, so you don't even need to swing the guard down.
Since yours is a "build" and you are using a trigger guard kit from yet some other maker, I have no idea what the specs they use are, or if it will fit.
Also, properly supporting the rear side of anything you are driving a pin into is just basic "shop sense".
Again, just to be clear, the rear hole (next to the pistol grip) goes all the way through and is for the roll pin (nom. 1/8" pin) The front hole, next to the mag well is a blind hole, does not go all the way through, because it is not a pin hole, it is a latch.
IF an aftermarket kit has you put a pin in the front hole, consider it permanent, because the only way you are ever going to remove it will be to drill it out.