Maybe some ideas here. https://www.advrider.com/f/threads/66-matchless-g15-and-soa-eagle-sidecar.1435574/
I agree with the description. I had a 1951 BMW R51/2 with a Steib sidecar that I imported from Athens Greece. The brakes and suspension were marginal riding solo without the sidecar. It shook badly on bumps and swerved at the suggestion of braking (which is all it had anyway). I remember when I had a friend riding hack and was pretty spooked whizzing closely past the parked cars until I remembered to move over a bit. Best of luck, I'm sure it's better than mine was. I rode it around Athens for a few months then shipped it home to CA.Took it down the road today, it's like a scary carnival ride! LOL Put it the basement and ck'd dimensions to find a lot changed when I put the weight in the car and my ass on the bike seat. Made adjustments , added 1 inch of toe in, raised the rear of the car. What a difference! I'll leave it alone till i get the new tire from fleabay next week.