Yup, all cars were single circuit up to the mid-60s. It’s actually a pretty good system the only addition really required would be a brake fluid level warning light. Failures due to wear are “friendly” in that the pedal goes soft well before disappearing. Now, if a rubber hose fails you’re pooched but they give lots of visual clues before failing.
However, maintenance and North Americans never did go together very well so they mandated dual circuits to protect idiots and the clueless. Generally it’s always the front circuit that fails. This leaves just the rears, and rears that probably also have been neglected. Not really any better than the emergency brake so why all the bother?
Anyway, VW single circuit masters all failed in a predictable pattern, giving lots of warning to the owners. However, when they switched to dual circuit, it all changed. Everything will be fine and then the pedal will go straight to the floor. It’s about the most scary thing imaginable. If you have the presence of mind, you can release the brakes and they may well be normal then. But that takes incredible mental discipline, usually you just press, uselessly, harder.
All that to say, a VW dual circuit master wouldn’t be my first choice if was converting to dual circuit brakes. The OEM Triumph masters are good.
Myself? I stayed single circuit. Works great. Bleeding is stupid easy and I just perform regular visual checks.
YMMV
