PS12 Trapezoid front brake cylinder

Hi! Looking to re-furb the above but the re-build kit (GU28659300 10.4090.20) is not available from GutsiBits and I was wondering if the PS12 round reservoir version would fit? Also I’ll need a new gasket for teh rservoir top.
Any ideas or is there a way round swapping the master and reservoirs for the round ones? Looks a bit difficult as it all obviously bolts to the switchgear and brake lever. I guess someone must have had this problem before.

Is that trapezoidal unit made by Brembo or is it a Magura unit? I suspect it is the latter. My 1988 Cali 3 started off life with one, but it now wears a more modern Brembo rectangular and replacement right hand switchgear as it is all part of the same.
Repair kits are available for the Magura unit as it was used by many manufacturers (Even my Harris Bonneville uses the same unit).
You can get a newer rectangular master cylinder used on the K series BMW’s of the 80’s, but watch out as they cover the mirror hole.