If the sheet angles up from the lead block to the winch too steeply, it will inhibit the backward movement of the car. You would definitely need a rope handle on the car to move it aft... or you can try to keep the line angle low... with a second block on the track, or perhaps a foot or cheek block on the coaming to guide the sheet to the winch... heck... you may not need any of that stuff.. since you don't really have any purchase on the control line... there will be very little friction to inhibit the rear movement. On your simple system, a rear pulling bungee cord will help the lifting sail pull the car backward no problem. If you decide to add some purchase to system.. the plunger pin hole might be modified to hold a single block with a becket.... then by adding a double cheek up front you could have a 3:1 system. But as it is, I think it's a pretty cool upgrade... you will find yourself trimming that headsail a lot more because of the added convenience.
