HJ can be the most frustrating when trying to figure out what is what. HJ saw the most changes through the series, but given HJ ran for a fair time (9/74 through to 5/76) I suppose it isn't surprising. Major changes affecting Sandman that occured during HJ:

Armrests became part of XU3 and XX7 on M70/80,
Carpet added to XX7 (and later XU3) on M70/80 (needs more docs).
Retractable seat belts.
M80 based XU3 and XX7 dropped.
Reduced GVW Sandman added (XX7).
3.3L engine became standard.
Front discs became standard.
Plus a heap of restrictions on autos, and what and how you could get them.
Intermittent wipers became standard with V8.
3 x trim styles/colour range.
2 x paint charts.
Introduction of canister from 1/75 which meant a different carby and fuel tank, ending the requirement for an auto and manual carb as carbs were now the same for the same engine.
Introduction of ADR27A as a trial meaning totally different engines.
Change from GTS fascia to a black Holden/Belmont/Kingswood specific fascia.