FWIW, I use the AP Racing CP3125 master cylinder on my 79 Jota with original disks and calipers. It retains the more or less classic look but works oh so much better than the original brembo, no friction problems and a nice progressive feel. You can tweak the ratio, supposedly the equivalent of 16-19mm cylinder, but I find it feels more like a much smaller diameter than that. Unfortunately they're not cheap (mine was retired from the racebike after the Phillip Island whoopsie-daisy) but are a good option. They also do not have a mirror mount if that matters to you.
