Reply to neil:
Congratulations on saving a bit of your history Brant. For your questions:
Pony Motor: Carb getting rebuilt and new spark plugs purchased
What gap should the spark plugs be? - I don't know, someone will, but starting at 025 is probably a good starting point.
Grease gun 50303: Where can I purchase one? Someone may have one to sell used - try posting a Want ad in the For Sale section of this forum. You can also buy an adaptor for your normal grease gun to enable connection to the larger fittings some of these tractors have. You just need to not apply any pressure as the old greasers applied very little pressure as the seal design meant they could be damaged with higher pressures
Engine Oil: Still shows full and good color. Do I need to drain and refill? You should at least take a sample from the drain plug to check for water and other contaminants that may have settled. Drop 8oz out to be confident. Weight and quantity? The original service guide probably recommended 30 weight and if you want to, you can look for non-detergent 30, but you can also use "regular" modern diesel engine oil I think (someone will know if any of the modern additives are harmful to engine components, usually bushings and bearings) - just be prepared to change the oil filters early in case the oil's detergents dislodge accumulated crud in the engine
Engine Oil Filter: I believe its 2A2473, any good places to purchase these? Try your Cat dealer - he may have superseded this part number. Also search this site for aftermarket alternatives
Fuel Filter: I'm not seeing a filter anywhere in the parts book, just the "element" assembly 6B3447, should this be replaced before starting? The element is the filter - it's basically the filtering element that would be inside a modern disposable filter. By all means replace it before starting if you want, but I'd almost be inclined to leave it in to catch the crud that has inevitably settled on the bottom of the tank, and then replace it after catching all that crud. If you can't get fuel pressure, then you probably should change it
Am I missing anything else? All help and advice is much appreciated!
Welcome Brant, just have a quick look inside the fuel and oil filter housings, you may find that the original brass re-usable filters are in there, they were designed to be washed and re-used, if you find more modern disposable filters in there, get the part numbers and go buy some.
Look on Fleabay for a copy of the Operators booklet on the RD6 tractor, and buy it, you should be able to get one cheap, that will have all the good info you need for proper servicing and adjustment of that tractor, like the filters, and carb, magneto, clutches, brakes, etc. I have one running RD6, and a couple of project tractors, and really enjoy driving mine.
Oil pressure is critical before actually letting the engine start, if you have doubts about how good the oil gauge is, get a known working gauge, and plumb it into your oil system.
The later built RD6 were called a D6 by Cat, but when you buy the operators book make sure you get the one for the 3 cylinder diesel RD6/D6, engine and frame serial numbers start with 2H, and not the later 6 cylinder D6 models, starting with 4R/5R or 8U/9U.
I use either straight 30W or 40W engine oil in mine, what ever I have on hand, as others has suggested, check all oil compartments for condensation before starting the tractor and moving it, I like to have a suitable piece of wood to put over the air intake, like a piece of plywood, after removing the mushroom shaped cover first, if the engine runs away you need to move fast, with the minimum chance of screwing up.
Good luck, enjoy the journey
Mike