I just finished a complete rebuild on my 53 3/4 ton, used dot 3. It's cheap, easy to find and has worked just fine in this old truck for past 50 plus years. As stated, blead the thing with fresh fluid every year, you'll be fine. Oh BTW, I made a pressure bleeder from a 1/2 gal. garden sprayer, makes the job painless, blead the truck inside of 10 minutes by myself.
