The Bendix Hydrovacs are named by what 'series' they were... literally 'series one, series two, series three, etc'. Yes they had part numbers, but the evolution of the 'vacs were classed as the 'series'.
Oddly, series one (the oldest) and series three and four 'vacs can be rebuilt quite readily. The second series 'vac (early to mid 40's) are the ones that are hard to find rebuild kits for. I got two, both from England.
I have rebuild manuals for the series one, two and three 'vacs, but parts are a little hard to find.
Midwest Power Products (google them) is the go to place for 'vacs... dude knows his stuff.
As far as brake upgrades, its more important to run dual circuit brakes than disc. But there are few guides on splitting the single into a dual circuit... most who want dual circuits run dual 'vacs (like mobile homes did).
