Thanks for the responses.

There are no threads left to come into contact with the top or slotted portion of the castle nut (which is also threaded), but it would seem to me that inherent in the design of the nut that the "grip" lost there would be minimal.

If I could get it high enough in the air, I'd go the BFH route, but I don't have enough clearance under the car to really wail on it.

Ran it 100 miles yesterday. Alignment actually seems slightly better than before the axle swap, but I think I may need to balance the tires. I wonder if cleaning all that CVJ grease off the wheels will fix that...