So its basically working now - I had to replace the pulleys I was using, since they were only held in place with M6 screws, and the rear one bent. I replaced them with a fully 3D-printed pulley with an M8 stainless steel threaded rod shaft, and that seems to be better. Had to crank up the 3D printer so it was printing solid with no infill, but the new pulleys seem like they should work. If not, I will try printing them with a TPU (fairly hard rubber) insert where the chain goes, and possibly replace the ABS parts with carbon fiber infused ABS. We'll see how it goes.
In any case, here it is in the basement, ready to start its first winter as an exercise trike:
I'll be building a new seat for it this winter, and painting it in the spring when it is a little warmer out.
Right now the issue I have is the trike is a little too short for me. What I mean by that is with the seat-back modification I did, the more vertical position pushes my shoulders forwards a few inches, and my elbows have to go behind my back to get my hands on the handlebars. Its not terrible, but I built this trike in order to have a comfortable ride, so I want it to fit right. I can't move the handlebars forward because they are currently clearing the tire by about an inch when I turn. I currently don't have any padding on the backrest part either, and once I add that this geometry will be worse for me. Its not too bad when it is going straight, but when I turn I have to really haul back on my shoulder joint, which is rather uncomfortable.
My current thought is I will give this trike to my wife (I was originally going to build hers next), and build a new one that has a slightly longer wheelbase. She is ~8" shorter than me, so she should have no trouble with this one. I think I will design a new frame entirely in CAD first, and make sure it has the parameters I want before I start building.