The magwell chutes for PC guns will not fit regular 3rd gen frames without gunsmith modifications.
The rear of the grip frame is machined for a pair of "legs" on the chute to fit between the frame and grip. The "legs" are then drilled so the grip pin goes thru them to affix it to the gun.
These pics are my PC 4006 IDPA model showing what the bottom of the grip frame looks like, with the spaces on either side of the grip where the magwell "legs" fit.
I bought my magwell chute
here