The master and likely everything else can be rebuilt by someone like Brake and Equipment Warehouse in Minneapolis,
https://brakeandequipment.com/ . Call them, do not go online and expect to find the answers for this old stuff. They have all the parts and the expertise to bore, reline and rebuild anything. No, I am not affiliated with them in anyway and I am sure there are other outfits like them scattered all over the country, likely the world. I have not seen them stumped yet. They almost certainly are familiar with this double line thing and have the answer as to what to do with it.
Here is what they say about themselves:
We have been supplying the Upper Midwest with quality auto and truck parts for over 55 years. We started as a brake specialty warehouse and have evolved into a full line automotive warehouse as we continue to meet our customers' needs. Located in the Beltrami neighborhood of Minneapolis, just off of Central Ave and Broadway Ave, we are able to serve Minneapolis and the surrounding area quickly and efficiently.
Our award winning machine shop separates us from the competition by offering custom friction work for hard-to-find classic automotive parts to industrial friction application. We do in-house, plasma cutting, custom brake hose and brake lines, brake shoes rebuilding (bonded/riveted), brake shoe arcing, flywheel grinding and cylinder sleeving for wheel cylinders/master cylinders and calipers and of course drum and rotor turning.
455 HARRISON STREET NE
MINNEAPOLIS, MN 55413
TOLL FREE: 1-800-233-4053
TEL: 612-378-3141
M-F: 8:00AM — 5:00PM
SAT: 8:00AM — 12:00PM
