Planters JD John Deere 494A Planter/Plates Setup Advice?

[Almonzo]

A few years ago, I picked up a John Deere 494A planter, along with a number of metal planter plates. Fertilizer bins are shot, but seed bins seem fine, albeit I am a bit fuzzy how the planter plates exactly should install in the seed bin base -- bins fold up, plates fit underneath, however there are two different sized metal discs, which fill in the center area, which I think the planter plate fits just outside of -- however the fit doesn't seem right. I have the manual, but unfortunately it doesn't provide detail on how the planter plates install.

Can anyone point me to video, pics, or other references providing more detail on installation of planter plates in a 494A? Or even mention what range of other planter models are similar in this respect, to widen my search?

Maybe separate thread better for this -- but also looking for advice on plate selection, for mixed sized corn seed (rounds plus flats; rather large kernels) -- also germination might be poor, so thinking to overseed -- would it possibly make sense to use bean plates? Yes, it's getting late in MI to plant corn, just want to learn the steps this year. Have several soy bean sets of plates, and the small and medium corn plates. Wondering if this planter is capable of using newer plastic plates...

Thanks in advance!