These big rigs hauled millions of tons of cargo millions of miles without too many disasters not caused by the driver or the other fools on the road. A well-maintained original brake system is going to be safe and reliable, particularly since few if any of the restored oldtimers will be worked anywhere near how they were used when they were new. Just don't take any dangerous shortcuts rebuilding the system.
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!