1965 Valiant brake woes

Kendog 170 said
Keep it cheap.
1968 PLYMOUTH VALIANT 3.7L 225cid L6 Master Cylinder | Shop Now at RockAuto
Then this only if needed. I'd keep the Proportioning valve.
Mopar '62 -'70 Adjustable Master Cylinder Push Rod

This seems like the obvious answer, but there's been so much wonky crap so far I'm afraid this will just reveal the next weak link.

Kendog 170 said
One question. Are those 1/4" brake lines on there or 3/16" ? Should be 3/16".

I'm not sure. They were installed by the P.O. There are no obvious markings and measuring the outside isn't close to 1/4" or 3/16".