Me and my dad build this frame. We needed a solution for the workbench that was behind it. So we made the frame that it would fold up. The pictures aren’t very clear, (the workshop is kind of a mess), but we attached the frame to the ceiling where it rotates. We also used weights instead of the strings, and we used a pvc tube to guide the weights. The chain also kept slipping so we made a bracket from an angle iron to keep it from slipping. On the top beam we mounted a led strip so the workpiece is nicely lit. I hope you like and maybe can use our ideas.
I really like your angle bracket chain keeper and chain rollers. Great use of available materials, and brilliant hack! I think I may do that on my machine too. Way cheaper than a 3d printer to make a chain guard!
Sewing machine bobbins available in plastic and aluminium.
Edit: The fastest and cheapest chain-guide you can get on both sides of the chain.
Edit2: Do ask the wife/girlfriend before using and compensate with a great candle light dinner. Credit for this idea goes to Jackie.