The distributor cap probably got some moisture in it when you pressure washed the truck. Remove the cap and spray some WD40 in and try starting it again.
I have a parts and service manual for a GP52. Everything in the manual should be the same except for the tires
If the truck is equipped with a fluid coupling that you only need to depress the clutch to change gears. If you just depress the brake pedal when stopping the truck will not stall. I also think that this truck has a 2 speed transmission. If you pull up on the shifting lever then shift that should be your second gear.
I would expect that most common items are still available for this truck.