Since Kimber doublestack .45 mags are so $#@! expensive and hard to find, I went the gun show today with a mission.
Magazines for the Para-Ordinance P-14 can be had for about $25, and are fairly common. I discovered that the ONLY difference between an aftermarket P-14 mag made by MEC-GAR and the factory Kimber mag is the position of the magazine-catch slot. The Kimber slot is higher than the P-14 slot. This allows one to widen the P-14 slot so it will work in the Kimber. The Kimber mag would be much harder to modify for use in a P-14.

Examining the MEC-GAR mag shows identical marks in the plastic floorplate as the Kimber factory mag. These are from tooling marks in the mold, not from machining the plastic. The metal bodies also show many identical marks.
On top of that, the mag follower on the factory Kimber magazine does not touch the slide stop. It will not hold the slide back after the last shot, or when working it by hand. The MEC-GAR magazines will