I've run long distances in a variety of LRs. The most comfortable (and easiest to control in the event of a tyre blowout) was my 127", a 1990 model just before the Defender name was introduced (and the 127 became the Defender 130). The long wheelbase made for a very comfortable ride over rougher roads.
My 90 on the other hand does pitch quite a lot, which can become tiring after a while.
The early 4 door Range Rover I owned for 13 years was the best for long distances!
I once did 250 miles in a SIII 109 station wagon (an ex-diesel a previous owner had converted to V8) - by the time I got home I could hardly turn my head my neck muscles had seized up...
With the '76 Mog, so long as I get out for a stroll every 200 miles then there is no problem doing long distances

Cheers,