I have a 1987 Cushman (not a Turf Truckster) with an OMC 22 hp engine. I've become somewhat familiar with Cushman Trucksters of that age, so maybe I can answer some of your questions. On the "Sillylittlecars.com" website you will find a few manuals that cover most of the late 1980's Trucksters for download. You don't have to be a member to download. The ...767 Supplement manual on this website contains the electrical diagrams for many models. If you don't find the exact one for your Turf Truckster, there should be one that is close. Find sources for your Daihatsu motor parts and you should be good. The main ...767 manual contains exploded views of the body and sheet metal parts. Sadly, none of this is available new any more.
Drivetrain and engine parts for trucksters can be found at
www.denniscarpentercushman.com and
www.directparts.com. I have also found that many parts can be found at auto parts stores, but they don't have a cross reference. Older workers can look at your old part and then find the same on the shelves. The newer guys can only find it if you have a part number.
The local forklift repair shops can be another source of parts. When these little vehicles were in use, it was the forklift repair shops that maintained most of them. I found my brake master cylinder at my local shop for about 1/3 what they want on Ebay.
Late 1970's Ford F-150 wheel brake cylinders are almost identical, so the rebuilding kits work fine. The F-150 wheel cylinder castings are the same, but with a bump on the casting that needs to be ground off.
Gas tank problems are usually internal rust and pin holes. These can be fixed with a tank relining kit from KBS Industries. The kit comes with an etchant to break up and remove the rust, a neutralizing solution, and an epoxy-like lining material. A few hours in increments spread out over several days will have the tank clean of rust and relined to make it last another 50 years or more. You need ways to seal the openings during treatment, and some fat pipe cleaners to clear the inlet and outlet tubes of the epoxy-like material before it hardens. I used a couple of hands full of gravel in the etching cycle to help break up the 1/2" or so of rust cake in the bottom during the etching cycle. That, and some vigorous shaking did the trick.
The wheels on Cushman vehicles look the same as what is readily available, but the lug spacing is slightly different. Some have bought these wheels anyway, and had a machine shop drill the Cushman wheel lug pattern in between that of the original. The benefit is that the wheels will fit either lug pattern. Most tire shops have, or can get tires and tubes for you, and they can mount them too.
I found that the mechanical fuel pump on my OMC was no longer available, except as New/Old Stock, and the rubber parts had deteriorated. I bought an off-the-shelf automotive electric fuel pump and added it to my Cushman. It never ran that good before the electric fuel pump was installed. A plate and gasket was made to block the original mechanical fuel pump location.
Tail lights and lenses are still available from auto parts stores. The gas cap was also available, but it's for a sealed system, and my Cushman needed a cap with a vent, so I removed the check valve in the new cap.
This should all get you well on your way. If you have specific problems or questions, post them here and I'll try to help. Cushman rarely made major changes in their models from year to year, so something from a few years earlier or later should fit.
Charley