Shorten the chains until you have only about an inch of side to side play in the mower deck. Then make sure you lock them tightly - they have a tendency to work themselves loose! Somewhere on my 10 qcres is a turnbuckle from my old L185. I never did find it. I painted the replacement Kubota orange!
If you are using R1s consider widening their wheels to the widest stance. If using R4s, maybe you should have some rear wheel spacers. Up north here we need them with R4s to allow tire chains, but that should not be a problem for you. I don't know of any issues with turf tires.
Finally, if the mower is old and worn, maybe the 3ph pins are bent out? Or possibly you have a mower for Type 1 and 2 hitches; use the inside slots.
Many of the members have gotten pin-adjustable chains from Hodge and are delighted with them.