The BDR uses a 1982 VW Vanagon master cylinder. with M10X1.0 ports front and rear circuits.
https://www.rockauto.com/en/catalog/...+cylinder,1836
You could add a proportioning valve to the rear circuit. Tilton makes a few in that metric size.
Valves - Tilton Engineering
M10 pre-made lines are plentiful at any NAPA store