So to double back to this and give an update, I ended up going with the early Viper master cylinder I linked above. I did have to modify the 4 bolt to 2 bolt adapter I bought to enlarge the center bore though. Needed to increase it about 1/4" overall diameter if I remember correctly. Also had to shorten my pushrod by something like 7/8-1". It seems to be a pretty nice fit so far, though I'm still working out some other kinks with the whole setup. I like my line routing much more this time around and ended up going with a simple tee for the front lines and an adjustable proportioning valve for the rears. Figured this gave me the most flexibility in both feel and routing. I think I still have a flare or two I might need to redo though. I rarely have any luck making them myself as lines always seem to slip in my tools, but I did buy a different style one that I will probably give a try the next time I work on it. Pedal isn't as solid as I had hoped it would be, but thinking some of this might still be down to tracking down any sealing issues as the various connections. Car stops fine though, no worse than before at least, so happy I didn't make backwards progress if nothing else. Found out that one of my rear axle seals had let go while I was in there, so nice to catch that before it caused any more problems.