Not exactly 'aftermarket' but I used a system from a late 70's GM car, probably a Gran Prix. Mounted the controller on the inner fender and the canister under the dash to operate the pedal directly and I am quite satisfied with it. I like those old simple systems with one button to operate it. It does not control the speed as accurately as the newer digital systems. Lose a couple mph going up a steep hill and maybe gain some going down, but it sure does help on a long trip. It might be kind of hard to find one of those systems now but this was late 1990's when I built it.
Mark
