Here’s a design for a uniform input/oscillating output mechanism. The important part is the rocker arm/slide portion.
This would run like the actual incline. Install at the top of the incline, tie a string between both cars, and wrap the string around the output. You’ll want to step down from motor -> slide and step up from slide -> output so you can get the cars completely down/up in one movement of the slide.
I built it to run loaders on a spacey blast furnace, but it should work for you guys too!