Banditfarmer: A friend had one of those drills years ago. The ground had to be pretty dry or the dirt would stick to the coulters and throw out ditches and not cover the seed. That is why the JD drills have the depth gauge wheel right beside the coulter. It keeps the dirt down and will not allow it to follow the coulter around.
You Oliver 1550 is not going to pull it very well. Even on your flat ground it just will not work well. Friend pulled his with a JD 4020 and it worked it pretty good.
Using a rotary mower on the stalks will make it a nightmare to get through this drill. The stalks will bunch up and not get cut. Then you will have drag piles in front of the coulters. It if the fodder is as light as you say then I would not touch them. While they are anchored to the root they will then cut better. When you mow them off they will then slide and not cut very well. Quite a few guys around be are just using a chain drag harrow on the stalks. If you do it when they are real dry they will get ground up very well and spread out too. Plus it is fast to do. The faster you go the better the harrow works.
Just some ideas.