I'm no expert on Kubota's, and especially a B1200. I'm hoping one of the experts will chime in.
1. The plow you want to use, is it 3 pt hitch compatible? Do you already have it?
2. There is a free pdf Operators Manual available at
WWW.Kubotabooks.com. It has no reference to the 3ph, so was of no use for this issue. It covers the B1200, B1400, B1500, B1600, B1702 and B1902 which indicates that they're all similar.
3. You can use the search function on this site to find past posts.
4. There is a user, Rosohatica, on here now from Croatia who has a B1402, which may have a hitch like yours. Perhaps you could DM (direct message) him for pictures, measurements, etc.
5. Could you post a picture of the hitch parts you have?
6. Here are some diagrams of the hitch on a B1700, which may be similar to yours.
Rod 060 slides through a bracket, which I think is already on your tractor. Based on a recent post, you may have to remove a wheel to install this rod. Then the stabilizer bracket 140, spacer 130, and lower arm 110 slide on each end, secured with a pin.
The lift rods are pinned to the lower arms and upper arms. The right-side arm is adjustable to allow for leveling or tilting the implement.
The top link is pinned to the bracket on your tractor and to the implement. Its length is adjustable to make the angle of your plow what you need.