The knobs under the dash are for the dump bed. The right knob is marked PTO. With transmission in neutral, and clutch disengaged while stopped, pull the knob on the right out. That will engage the PTO. Let out on the clutch, normally, pulling out on the left knob will raise the bed. If you are just dumping in a pile, pull the left knob out, and it will power up. Once it reaches maximum height, push knob halfway in for the hold position if you want to pull away from the pile, and completely empty the bed.
More than likely, it has power down too. If like mine on level ground, it raises pretty high and you'll need to power down some by pushing in the left knob until it stops, until gravity takes over. At that point, you can push in on the clutch, and push the PTO knob in. When the bed sets on the frame, pull the left knob back out to the middle position. The middle position should also be a hold position on the bed, if say you want to raise the bed half way.
If you want to tailgate stone, being it is a straight 5 speed ( not seeing a 2 speed rear end button or cable on the shifter ) it's probably geared low enough to take off and spread in 2nd. gear. Unless it's an air gate, the tailgate trip lever, if it has one should have a light piece of chain with a large loop on the end to put over the trip lever to keep it in place. There should also be a piece of rope on the trip lever. The trip lever should have a light snap to it going over center when the gate is latched shut. If it's worn as much as I think it might be, and it hasn't been adjusted up for wear over the years it probably won't take much to trip the gate.
Some manufacturers weld a little loop on the trip lever handles to hook a rope on using snap like on a lead rope. Or, have a hole in the handle to put a rope through. If you're planning on tailgating stone, you'll want a piece or rope, preferably soft nylon 3/8" rope approx. 36" long with a 6" or so loop on the end you'll be pulling with. This is extremely handy when tailgating stone.
If tailgating stone you'll want to set the chains so the gate opens, minimum 2X as wide as the stone you're spreading. You'll have to experiment with it depending on how thick you want to stone. Putting down a thicker base, or just top dressing. While setting still, raise the bed about 1/3 of the way up to make sure you have stone against the tailgate. If it will take off in second gear with a load on before trying to tailgate, place in second gear and get moving before pulling the trip lever. If you trip the lever before moving, you'll have a pile of stone you'll need to knockdown. Depending on how good you are on the clutch, if tripping from a dead dig it's been known to kill the engine and will be dumping stone in a pile until you get it restarted and moving. It's a learning curve if you've never done it before. More than likely, once you start moving you won't be able to change gears, due to gear pressure on the transmission with the PTO engaged. You'll just have to watch in the mirror and see how thick the stone is being put down and adjust speed from there.
The controls on the floor with dials and lever are for a salt/cinder spreader. If the PTO is engaged DO NOT mess with that lever. Just make sure it is in the off position and leave it there and set both dials to "0". If the lever is set in the engaged position with no spreader on, there's a good change pressure will deadhead against the pump and burst a hydraulic hose that goes more than likely from that control to the back of the truck, inside the frame. Not good if you have a load on and have to shovel it off until that hose gets repaired. That truck appears to be an 80's model, and a good chance the hoses are original.
Always be aware of tree limbs, power/telephone lines overhead when dumping, or especially tailgating. On a truck that size, the bed will easily raise above the 13'-6" legal height, but most residence lines aren't normally that high. It's not rocket science, just takes some common sense. Always be aware of what is overhead, and your surroundings.
