Radish seed is very similar to small milo seed. If you have e-sets use a small sugar beet plate. I believe it is a 1/16" hole sixty cell plate. Not sure about deere but I'm sure they have a sugar beet plate.

 We also have a 1790 and we are going to try several things, including mixes and alternating rows like you are talking about. Our plan is to put the legumes in the tanks and plug the splitters rows like you would plant 30" rows and then just fill the interplant small row unit  boxes with radishes. You will have to refill often but you should be able to get 3 or 4 lbs of radish seed per box. If this works we thought we would try to either make an extension for the small boxes or try to mount a gandy type air delivery system to get seed to the interplant units.

 The neat thing about the 1790 is that we can have several different strip plots by putting different mixes or crops in the individual boxes and changing the pop with the VRT hyd drives.

 There is so much that we don't know about these covercrops and the only way we are going to learn anything is to try alot of different things to find out what works best.