I'd decided to try a 3/4" (19mm) master cylinder for the twin piston dual discs on the '75. I finally found a good deal on one on ebay. It is from a 2004 GSX-R600. I'm not really liking the looks of the plastic fluid reservoir, but it is functional ugly, so I can live with it. It is a "radial" master cylinder, which just means the piston goes front to back inline with the lever travel. One nice thing with a radial type is the fluid outlet is on the bottom rather than the end.
The '75 used a pressure switch for the brake light, and I'd rather use a regular switch, so this will fix that. The fluid outlet has two alignment tabs, shown here. I ended up cutting one off to get the lines ran where they needed to go.
I'm running separate lines from the master to the calipers, rather than a single line going to a junction block and splitting from there. This means only one banjo bolt and two brake lines, as opposed to three or four banjo bolts and three brake lines. The new double bolt, with the single shown here.
The brake lines are 27" from Russell, with 10mm banjo on one end and -3 AN on the other.
Here is the -3 AN end with the adapters at the calipers.
The adjustable lever will be nice.