Planters JD 246 corn planter, are other plates available?

[Baranx4]

I'm going to pickup what I believe is a JD 246, 3 point, corn planter this evening, I didn't bring the trailer with me when I went to look at it or it would already be home. Fertilizer canisters are intact, farmer got ill this summer and had to retire never cleaned out the canisters. Fert on one side is frozen in place. Planning on cleaning it out and giving it a good soak to get rid of the rust and hopefully it will loosen it up.

Don't know much about planters, I read that the plates on the 246 are the same as the 71 is that true since I would like to plant more than corn?

Is there a manual on it available. I already saw the parts breakdown online.

Thanks in advance and expect more questions.