Awesome. I was going to make a single attachment point at the bottom that would be moved left and right by another motor and chain to give pull in the appropriate direction (down, or down/towards a corner). I was starting to think of making it not need a third motor and was starting to think about how to do it with block and tackle but looks like you worked it out already. I like the design and look forward to experimenting with it once I finally get to build my maslow! Nice work! I had all the same thoughts as dlang until I saw how you cross-linked them so the force grew greater towards the corner.
How many wheels are on your blocks to make it work out?