The screen shot below is the brake cylinder data you asked about for your '52 6400 (Utility) with Huck brakes taken from the 1929-57 Master Parts Catalog.
Rear-Front cylinder (1-1/2" diameter) GM# 5453866
Rear-Rear cylinder (1-1/2" diameter) GM# 5453865
Here are a couple of links to a site I found when searching more info on the original GM part numbers. Each page gives a long list of manufacturer part numbers that cross-reference to the original GM #'s. Further searching on the web for those numbers (I only did a sample check) show they are easily/readily available from various prices. The original GM#'d parts are also offered by Chev's of the 40's too. I didn't include the links but they are easy to find if you use the GM#s to search.
https://www.finditparts.com/products/3842904/raybestos-wc-14499https://www.finditparts.com/products/3842905/raybestos-wc-14500Your call on which vendor you wish to source them from. Happy hunting!
Dan
