Hey there Frik,
Glad to see a fellow South Afircan here.
I drive a 1979 hilux with a LS400 lexus motor, and a Ford Ranger diesel pickup.
I had the same brake problem, and it turned out to be the rear brake drum had a leak on the brake cylinder, which somehow bonded with the drum brake.
i had a couple of times where this just wouldnt release, until i had it fixed.
Also after all the years, the master cylinder inside the engine compartment, collected water vapour, rusting up the whole master piston. That gave me some hair raising moments, and had that fixed.
The lux now have power and brakes.
I have a HILEX....that is a HI lux with a LEX us motor