Is there any body of knowledge on converting 1960-1962 Valiant/Lancer to front and/or four wheel disc brakes?.
I haven't seen anything specifically regarding the 1st gen A-bodies. If the ball joints are the same as the 63-72 drum brake cars, you should be OK to convert to the KH disks.
Are there larger wheels necessary?
Yes. When Mopar began fitting disk brakes, 14 inch wheels were needed to clear the calipers.
Will a new/later master cylinder be needed?.
A later master cylinder is probably not necessary, but a new one probably is. I had a '66 with disk brakes. Kanter listed a different rebuild kit for the Disk cylinder than the Drum master cylinder. Disk brakes typically require more fluid volume than a drum system.
You didn't ask, but you will need a 65-66 disk brake proportioning valve if you stick with the single reservoir master cylinder. If you go to the dual chamber master cylinder, you'll need the appropriate proportioning valve, too.
I'd like the conversion to be as unnoticeable as possible from the outside.
There were two SBP wheels used on the early disk brake cars. Normal equipment was a 4½ wide, like the 13". If a Dart had a Rallye Pack, or a Barracuda had the Formula S package, the rim was 5½" wide. There's a noticable difference in the size tire that can be fitted to each. That's one place where it might be noticable.
If you're running hub caps, the ones from the 13" wheels should work fine on the 14". Wheel covers are a bit more problematic. In the case of the '66 Dart with disk brakes, they used the Coronet wheel cover.
