Is there a compelling reason to switch from drum to disc brakes? If the concern is difficulty in sourcing original parts, wouldn't it be simpler to swap to a later model, more available drum brake setup? Is the vehicle being used commercially, or has it become a "Cowboy Cadillac"?
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!