Engine swap, Bung a d24 into it

[Laird Scooby]

No, that would be the L28 from the 280C, detuned somewhat for the Patrol. The higher tuned version of the L28 with Bosch L-Jetronic to make the L28E was used in the 280ZX.

In terms of the diseasel engine, i believe they used the same one in the Patrol diesel as they offered in the Y30 Cedric/300C in Japan.

You're right, they did use leaf-springs and drum brakes on the 300C estate but in some models you could wind the tailgate glass down - it was really meant as a utility vehicle rather than a luxury estate i think.
I can't remember if they used a Watts Linkage, Panhard Rod or any other form of stabilisation on the 300C estate live axle, i'd have to do some research.