I've been waiting to graduate college for the funds to finish my 1969 K20 I started a few years ago too.
Attachment 99741
The dump package was dealer installed in 1972, along with the dual saddle gas tanks. It was a fire dept. work truck in Livermore California up until about 10 years ago.
It's an "electric over hydraulic" pump system, so all I need is a switch to operated the bed. The pump doesn't need to be hooked up to the engine, only 12 volts. From what I understand, the cons of this is that it cant generate a whole lot of lift. Still though it's just a pickup, and I have dumped loads of up to 3500 lbs with it.
If you're interested I have some closer pics of the hydraulic system.