Swetz,
If helps make you feel better about powershift transmissions. They have a long track record of being on TLBs. They are actually the high-end transmission option as they provide some nice features. As with adding any gizmo, the more complexity does open the door for more opportunity for something to break, but I personally would not be scared of a powershift on a machine with this pedigree. If it was a high hour machine with unknown maintenance and with signs of a hard life, that could be of concern. In this case, it appears you are getting a machine, that with proper upkeep and maintenance, should last you a very very long time.
As for parts, I would suspect that the New Holland powershift of that era would share many parts with an European Case M series powershift. As you noted though, the New Holland instrument cluster is probably unique.
As for transport, it appears you have everything set. However if that falls through, I think you need to reconsider your retirement mathematics.
130 miles, with a backhoe with top speed of ~24 MPH is roughly 6 hours transport time. Now the impact to your back/body driving a vehicle with no suspension other than what is in the seat and tires, is something to be concerned about!
Which actually brings up a point, are those 20+ year old tires on that machine? Not that those would not work for you, but in my experience tires tend to get hard and want to develop cracks over time. Just something to keep an eye on.