Hi Artur, All pre-war BSA sidecar chassis were of "A"frame construction NOT square or oblong. Also BSA sidecar chassis were fitted with fittings that fitted straight into the tapers/fittings on the bike, so no extra fittings were required. Also to the best of my knowledge BSA sidecars were all steel bodied, although I have come across BSA sidecars that have been re-skinned in aluminium because the steel has rotted away. The shape of your sidecar is similar to a pre-war BSA sidecar but the front of the passenger compartment would be a regular curve if it was a BSA and not pointed. Sorry if this is bad news. Regards Alan