Volvo 240 master cylinder?
Goggle suggests it's 22.2mm bore
but this perhaps indicate a 22.2 / 15.75 set up. No info on stroke.
http://seekpart24.com/volvo/240-p242...der-100026#all
Also read page 7 of below. It seem that the twin circuits were split diagonally and the twin bore set up was to reduce pedal pressure if one circuit failed. So I guess both circuits have the stepped bore and it is not a method of setting up brake bias.
http://www.volvo244.pl/images/broszury/1978-240.pdf
Another option?
Kerscher sell a 20.64mm cylinder to suit porsche brakes. It is an ATE unit from a Renault Traffic van. ATE part number 03.2120-1142.3
If I recall correctly.... the bug master cylinder has quite a long stroke. I always assumed this was to allow for poor adjustment of the rear drums.