Case 442 clutch/ fan mount nut

[IBC]

I am restoring an early 442 (I think a 69) I started it up yesterday for the first time in 15 years. The fan came loose. If I tighten the fan up all the way the "collar" nut tightens the clutch to the point that there would be no disingaging the pto. question is....should I be using a lock nut to hold the fan on or shims inside the collar nut to keep it from pushing the clutches together when I tighten it.
My book only shows a bolted system for the fan.

 

[IBC]

Update:
I installed it with a lock nut and it seems to work fine, I will know more when I mount my mowing deck. Ed