The operators manual recommends that there should be between 8 to 10 inches between the frame and the ground with the cutter bar in operating position.
The slot in the drawbar clevis is designed for a pin with a cotter key to secure the chain; the chain should be free to slide in the slot.
Since the drawbar on our tractor is upside down, a nut, lock washer, and bolt were used to secure the chain in the upside down drawbar clevis after the frame height was set.
Reviewed the 350 And 450 Mowers (Serial No. 800001- ) Operators Manual OM-E79838 Issue C9 under the Attaching and Detaching topic on page 15.
There is a notation NOTE: On 850, 950, 1250, and 1450 Tractors, attach eyebolt (G) to hole in mounting plate (I).
Unless you are using one of the four models listed in the notation, the mounting plate is not required and an eyebolt in the drawbar will work.
Hope this helps.