The slip clutch is nothing proprietary or OEM specific. Any that will fit your PTO and gearbox shaft sizes/splines will work fine. Tractor Supply or AgriSupply, etc., have them. And I doubt you would really need a laminated tailwheel. My FIL has a late-model BushHog Squealer 5ft with that same tailwheel (and just a blade mount bar - no stump jumper). It looks like it will hold up very well over a long time. If you really expect to be running over stumps or rocks, a stump jumper would be a worthwhile enhancement. I see no reason why you couldn't swap the bar for a stump jumper provided that one could be sourced. Just be aware that the mount to the gearbox is usually a BEAR to get apart!!
Also be advised that slip clutches require a once-a-season maintenance routine to intentionally "slip" the clutch disc to ensure that it's not frozen by rust/corrosion. Not a big deal; wife and I can usually do ours in about 15-30 minutes.