Greetings GoCateGo: Welcome to the vintage Airstream hobby. Such fun and you will learn patience in spades.
My son has a 69 Globetrotter, and it is plumbed similar to my former 66 Trade Wind. But actually you don't need a diagram. Plumbing is just putting water where you want it. The pressure in the lines is typically 40psi and the flow is typically 3 gallon per minute. The lines are 1/2" PEX.
Your trailer has a fresh water tank above the floor under the front window. There is a 12v
pump drawing water from the bottom side of this tank. There may be a couple of valves there so you can fill the tank with city water is you want. And a valve so you can drain the tank. Find these items. I eliminated them as we don't use them anymore. Modern water pumps have a check valve built in them so when on city water, you don't push water backwards through the pump. If you have an older pump, then you have a check valve downstream of the pump to prevent backflow.
Now what is next? Your pump pushes water toward the galley sink cabinet. It only pushes cold water. You have a water heater under the sink cabinet, so you have to tee in and fill that water heater. Then tee in and feed the cold side of the sink faucet. Plumb the water heater output to the hot side of the water faucet.
Now carry the hot and cold lines on down the trailer, through the closet to that wonderful wet bathroom. Plumb hot and cold to the sink faucet, which also serves as the shower faucet. And lastly a cold water line to the toilet.
There is a city water inlet hose stuffed in the back of the trailer. This is what you hook up when on city water. You will need to tee this line into your cold water plumbing system. Then you can run the pump for fresh water you carry with you in the trailer, or hook up city water and use that. You need a check valve in this line to prevent your pump from pumping all your fresh water onto the ground out the city water hose.
I use PEX plumbing system with cinch clamps and PEX fittings. Much easier than sweating copper tubes.
Again, just put the water where you need it. Drain plumbing in ABS is another whole subject. And one you will want to address as your trailer, like my son's, doesn't have a grey water tank. You can't run wash water on the ground in any campground or government land.