Trying to get it going and found this

[HRD]

Pulled the master cylinder off my 51 GMC that I'm going through checking just to get back on the road.
Truck was last tagged in 1969. I found it in a barn in the early 2000's. Had it towed home. Put a fresh battery, points and a gallon or two gas in it and fired it up. Ran good I thought. It has a Chevy 235 from 58- 62 as best as I can trace the casing #'s.
No brakes though. Made a few rounds in the back yard with 3 tires that would hold some air and a flat, then backed it into it's new storage shed. 18 years or so has gone by.
Time to get it going and back out on the road. Decide what I want to do from that point. First, just get it going and stopping.
Piddled with it since fathers days. Same routine as above except fresh gas from a temp jug. She woke up.
Has a miss but I'll do a complete tune up and oil change before I try and drive her.
Brakes!, got to have them. Put new shoes, springs, adjusters, wheel cylinders and cylinder lines on and decided I'd pull the master today. So glad I did. This is what fell out when I pulled the bore cap off.
This was all in the bore. The fluid and inside the reservoir truly looked good.
Ran out of cleaning fluid, so decided to finish when I pick up a rebuild kit. Lucky me, the cylinder bore looks good with no pitting so for. (the pics are when I first broke it open) So glad I didn't try and bleed these brakes yet. This crap would for sure plug a line.
Going to break the lines at the wheels and blow them out good before I proceed.
Anything else anyone know of I should look at on these brakes that I might be missing?