Land Pride makes both forward and reverse cutters, definitely go with the reverse cutter. Their forward cutters are models that start with RTA. I think you'll do great with the 50 incher. Mine came with the slip clutch, but my tractor doesn't have as much horse power, so when the tiller binds, it shuts the tractor down. I've even tore apart the slip clutch and scuffed up all the plates per manufacturers directions, it still doesn't slip when bound up. I don't think I have enough torque to spin it. I'd bet I couldn't shear a pin either. I do have a steep angle on the PTO shaft when lifted, so I just depress the clutch and disengage the PTO before I pick it up.
Whatever you do, do not add sand to clay soil!!!! Despite wanting a sandy loam soil, don't think that sand is your friend. Sand + clay + heat = BRICKS! Stick to organic matter only. Manure, compost, peat, leaves, grass clippings, etc. are your friends. We have clay soil here, and have at least 2 active brick manufacturing facilities close by, with several more that have closed down over the years. No sand for you!!!!
Let us know when you pick it up, and how you like it. I think you'll be pleased.