My 1983 GMC (Diesel) Suburban had a power brake booster that used the steering pump. The older diesels do not produce enough manifold vacuum (it's an efficiency thing...) for a standard power brake booster.
My '05 GMC 4500 has a combo power brake/power steering unit. Heavier, (1 ton and up) Ford trucks use a similar set up.
Early diesel Cadillac Eldorado used Hydorboost. Thats the system that I have on my 32 Chevy....Works great with a hot cam that produces low vacuum and easily adapted for under floor mounting. You car read more here. http://www.jpeater.com/techspec/hydroboost.htm