The simplest and safest "upgrade" is to rebuild everything to "as new" original condition, unless you've got a degree in automotive engineering and a research lab to test the modifications you make. If single-line brakes were actually as unreliable and dangerous as people say, there wouldn't be any old trucks left for us to tinker with. They would have all been wrecked because of failed brakes decades ago. I've seen some older Class A motorhomes with a dual line master cylinder and two small hydrovacs, one for each master cylinder chamber. No, they did not work well, and they were a nightmare to work on!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!