Looks like a nice concept. I like it.
A few questions though. The Gearboxes appear to be floating in space, do you have a planned attachment method yet?
I’m not personally a fan of running the chain over 8020 cross bar on plastic. I’ve seen it done before, and it works, but my team had issues in 2008 where we broke through some plastic this way. Make sure you get a strong delrin to rest on the 8020 bars.
How do you intend to tension the chains with the plastic blocks? If you slide them, you’ll shorten the chain on one end, and lengthen it by the same amount on the other side, and it won’t tension.
I like the use of 8020 for a test bed, nice and versatile and easy to work with.
If your unsure of using e-clips or cotter pins, definitely use e-clips. Cotter pins are relatively bulky (for this purpose) and believe it or not they’re harder to remove than e-clips. Cotter pins are also a pain if the bend because they stick out. e-clips are a lot cleaner.