With our 69 convertible, which uses the same internals as your 68, the windows are controlled by a string on a few rollers that uses a little bar type thing that mounts to the bottom of the window. The mount is moved up and down via a small toothed piece that looks like a jack stand. To my understanding, the kits used just replace where the rollers mount but are expensive. I don't know anyone who has tried this and I've only seen it done on insane resto-mods but, with having the door panel off recently to get the rear quarter window back on track, I can say you have to run the power through the door jamb into the dash at the firewall above the trim tag where there is ground out and you can put a small power inverter there as well to take in and send power out to accessories.
