That's a pretty old tractor...might be difficult getting a manual, but good luck!
As far as the oil capacity, I suggest you contact your local Deere dealer's service dept. They probably have a manual and can provide the capacity.
You'll want a filter anyway, so a visit to the dealer might be a better option.
If the dealer doesn't have the information (which would really surprise me), check the oil level...if it's filled to the correct level (on the dipstick), find an empty 1 quart container and go ahead and drain it in a clean pan (but NOT the 1 quart container). Then you can determine how much oil you've drained using the 1 quart container (pour the used oil in the container, then empty the 1 quart container into another pan or whatever you intend to use to dispose of the oil.
Just keep track of how many quarts...and write that down for future reference.