Really like the looks of that sidecar body! I'd love to see more pics of the build if you have. A bit confused by the swingarm from these pics, brightness of paint makes it difficult to see definition. Curious what that cylindrical thing in front of the car's shock mount is, almost looks like it has wires coming out the bottom and passing through a grommet into frame.
Have you thought about adding a diagonal brace inside frame box from right front to left rear at chair's wheel, to help control flex and distortion?