I had a 1983 Yamaha Venture Royale with a California Friendship side car, it handled pretty bad when I first bought it, but followed the instructions on how to set toe in and what a difference. Most sidecars aren't set up properly, so they track and pull side to side. There is quite a bit of math and measurement involved in the setup of your toe in and front to back placement. You also need a steering damper, (way different than a traditional one) setup from the lower fork to the sidecar mount, mine came off of the right caliper mount to the front frame of the sidecar. It appears his has one on the right fork lower, attached with a clamp.
The rig also had torsion bar suspension which would bounce over bumps, so I modified it to have a horizontal shock attached to the frame with a lug, and the torsion bar mount so it would rotate and compress the shock. Wow, did that smooth out the ride. It was a good riding, and good handling machine after that. I kinda miss it lol...
Charlie