I picked up a set of Gran Torino mirrors from e-Bay, and discovered the difference in the pedestals as well. Last weekend, I swapped pedestals (my stock Mach 1 onto the Gran Torino's housing).
Unfortunately, it's a bit involved. The cable controls are spring-loaded, and permanently assembled - meaning, there's no easy way to disassemble the mechanism in order to perpetuate an easy swap.
What I did was clip the cables inside the mirror mechanism itself, as to remove the cable from the housing. Then I compared the two pedestals and noticed the housing mounting surfaces are identical... as is the hardware holding the housing to the pedestal. The housings are identical (different part numbers, of course) with the exception of the shape adjacent to the pedestal mount - the Mach 1 is flared a bit more for more flow into the pedestal than the Torino housing. This is not important to me, because nobody's going to be climbing under my passenger side mirror and deduct points, let alone really give a crap once the paint is matched up.
After clipping the cables, I removed the cable from the Torino mirror pedestal and housing, separated the housing and pedestal, and drilled a 3/8" hole between the mounting holes on the Mach 1 pedestal. For the purposes of getting the parts painted, I reassembled the Torino housing to the Mach 1 pedestal and put the Mach 1's non-remote-controlled mirror assembly back in.
Interestingly enough, the remote-controlled mirror assembly from the Torino mounts into the housing exactly the same manner and location as the non-remote-controlled mirror assembly from the Mach 1. So if someone were to simply drill the necessary holes in the correct places on the pedestal, housing, mounting plate, and door, one could simply remove the remote control cable and mechanism from the mirror and swap them into their '71-'73 Sport Mirrors.
Before I took the mirror apart, I temporarily hung it in-place on the door, and ran the cable through the door, A-pillar, and through the dashboard to the driver side. It reached all the way to the steering column, but not much further, if at all (again, just kind of spit-balling the length to decide if I even want to do this, at the time). I remember seeing a picture of a '71 Cougar with remote in the dashboard just to the right of the steering column. I don't think there's enough room on the Mustang dashboard by the wiper controls... but I'll figure something out (maybe just relocate the cigarette lighter - I'll only be using it for a power source anyway... most likely just put it in the console or something).
The only hard part is getting the cable removed (intact) and/or reassembling. The cables at the remote control assembly inside the mirror have really small crimp-on cable ends - very much like the ones used on bicycle cable brakes (which is what I'm going to attempt to put it all back together with after I get the car back from paint). If it works, I'll have a detailed write-up with pics... if not - well, then consider this my attempt and potential failure.
FWIW - I also had purchased a Mustang II passenger side mirror with remote control... and still have it. I'll dissect it and see if all the mounting and whatnot is the same - if so, you should be able to make it work with '71-'73 Sport Mirrors... after going through the hassle of what I'll be writing up very soon.
