Never worked with an old JD, but should have likely 2 places it has different sprockets and or different gear sets to change the spacing. Setting both places gives you many different spacings.
A manual with a planter, baler, or combine is a really, really good thing????
There are very many helpful bits here, including a PDF parts manual. If you are interested in the planter its worthwhile to copy and past these links. If you are like someone yesterday and too lazy to bother pasting the links yourself, then god help you.
I'd sure buy a manual for a planter I wanted to use, there are too many adjustments and setups to try to just wing it.