I use a 855 John Deere and a 4 row 71 flex planter worked fine behind it. I couldn't fill it up with seed, but otherwise. it worked great. I sell these planters on ebay-do a search for corn planter .
You can take a look. The 4 row model with a light duty hitch weighs about 800 lbs, so your Kubota would be able to handle it with no problem and you could add liquid or dry fertilizer.
You are correct that most of the guys I sell planters to, spread dry fertilzer and work it in, as these planter units are not good for no till planting.