I worked on an '80s Chevy chassis school bus that was about a 60 series (similar in length, weight, WB, tire size, etc. to my 1965 60 series) and it came from the factory with a big ole' vacuum boosted dual circuit master cylinder. Looked and worked exactly like a super sized version of what's on a car or pickup truck.
So that leads me to believe that retrofitting an 80 year old design single circuit, split master/slave cylinder brake, to a modern day dual circuit setup (granted, I am broadly assuming a competent conversion with all new lines, prop valve, and etc) using parts you can get anywhere, would be anything but a positive.
However I don't want to sell @HotRodLincoln short on his point that a badly done conversion would be unsafe.
Then again, I see these folks in the Skoolie forums making their buses up to 18" taller, with wildly variable welding and engineering skillsets behind those roof raises, and I think that adding a modern day master cylinder would be a lot more doable of a conversion/update.
