Although they look similar, I would still like to see confirmation that the Polsten's master cylinder is the same as the Ford CMP master cylinder.
The CMP Ford part number is 91T-2140. According to
www.MacsAutoParts.com this was used for 1939-1952 1 and 2 ton trucks. They sell a rebuild kit for the same applications as part 91T-2004-A. The prices are for the master cylinder $69.95 and for the kit $32.00. (Rock Auto lists a rebuild kit for $16.50 for the 1940 Ford 91T truck 1-1/4 inch master cylinder)
The same master cylinder was used on the 2 wheeled CMP 15 and 20 cwt trailers (GS, pole, gas welding etc.)and the 4 wheel trailers for Brake Drum Grinder, 60 ton press, QMG-MT as well as GS.
All in all, it seems a common master cylinder, it looks similar, but before I suggest anyone to go out and buy a kit for anything as critical as brakes I would like to see confirmation that the Polsten manual lists the master cylinder as having part number 91T-2140. If you want to buy a kit on spec, I can't stop you. But if you do, please measure all the parts very carefully to be sure they match what you need. I don't know the weight of the Polsten setup but I'm sure its enough to be a menace if it gets away from you