Hello the sidecar is a right side monza. The BSA is a 1953
Hi Clyde
I did not realise that Watsonian made a right side Monza - I bet the mudguard is rare!
I fitted a Monza (left hand) to a Matchless 650 a couple of years ago and it was fairly straightforward. I picked up most of the fittings from ebay and bike jumbles.
You will need to check the fork springs are for sidecar use and you will probably need to fit a smaller primary and/or gearbox sprocket.
Another issue may be checking that the kickstart has enough clearance.
If you have a sidecar brake then things may get interesting as the pedal normally sits next to the bike rear brake pedal so you can operate them both at the same time with your left foot. With a left hand braked chair you will be using both feet to brake
Good luck with the project and keep us posted.
Jim