For Magman clutch

If the friction disk is installed backwards (Torsion springs to the F.W.) the disk will hold out the plate about 1/4-3/8 inch and cause the symptoms you describe!

As My thinking puts it together, the thinner the disk, and the more worn (or machined) the surfaces of the F.W. or P.P., the less the fingers will be pushed inward as the P.P. is tightened to the F.W.
This would "tighten" the adjustment and cause near zero freeplay at the pedal.

When every part is factory spec. new the fingers are compressed deeper into the P.P. This condition will result in the linkage needing to be lengthened to reduce freeplay. Yours needs to be longer yet!

As clutch surfaces wear (or disinegrate) the freeplay becomes less and less, till it is gone and the clutch slips.

I'd use a straight edge to check the depth of the fingers on a different tractor (both compressed with the clutch depressed, and with the clutch engaged, pedal out),Then compare it to the reluctant one.
Wish I was there!
JimN

LPS is usually found at autoparts stores, NAPA has had it as well as many others. Hardware stores also carry it especially those serving a broad customer base not just suburbanites.

Good luck, my Email is open.
JimN