The pic of the backing plate shows two adjuster slots at the top- - - - -definitely Huck brakes. Each shoe must be adjusted individually. Inspect all the wheel cylinders for rust pits that might be allowing seep leaks of fluid. If complete wheel cylinders aren't available, just purchase the right diameter rubber cups ands rebuild the cylinders yourself. A ring of rust pits in line with the fluid hole in the wheel cylinder isn't a disaster- - - -the cups never move back that far during normal operation. A good machinist can install a stainless steel sleeve in a wheel cylinder that will never rust, and that cylinder will last three days past forever.
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!