"where do I get 600-weight oil and how much?"
If memory serves, you'll need three gallons.
Your local NAPA dealer probably won't have 600W, but any industrial lubricant supplier should.
Look in the Yellow Pages and make a few phone calls to see about availability. I'm pretty sure Grainger keeps 5-gallon pails of 600W in stock.
And no, you're not crazy for owning a Fordson; remember, at one time, three-fourths of all tractors sold in the US were Model F's!