My father-in-law just purchased a Schwinn Caliente that's in amazing shape for its age. It has the Shimano Positron shifters on the stem and the FFS cranks. It's my understanding that the positron has the indexing in the derailuer and not in the shifter. If this is the case, will an old-school friction thumbshifter work on it? Or do you think that some Paul Thumbies would be compatible with the shifter?

On an unrelated note, he's wanting to change it over to alloy quick-release rims. But based on the photos I've seen, I'm not sure if that will work or not. At least not without replacing the whole drivetrain. I'm not sure the bike is worth that.

Here's some photos just for kicks.