This is all from memory (different parts for twin headlight clip):

Nose panel:
Premier, BO6, SL/E.
XX7, XU3, GTS (cutouts for air dam).
Deville (holes for badge).
Caprice (holes for upper grill piece).

Grille:
Premier, BO6.
XX7, XU3, GTS (different painted version of above).
SL/E.
Deville.
Caprice (same basic plastics as Deville, different paint and different stainless).

Bonnet:
All HZ except normal 1-tonner.
Caprice (holes for emblem).

Guards:
XU3, XX7.
BO6 (same as XU3, XX7 but has holes for RTS badges).
Premier (holes for Prem badges on rear lower and holes for side strips).
Deville (same as Premier except badge holes different).
SL/E (same as Premier except different badge holes).
Caprice (same as Premier but no badge holes).
GTS (fluted and GTS badge holes up high, rear).

Surrounds:
GTS, XX7, XU3 (black paint).
I think the rest are the same.

Support panel:
Should all be the same, except Premier and Deville will normally have A/C holes for plumbing. Be aware of differences with early HJ examples as there isn't much difference in twin supprts HJ-HZ bar early HJ was slightly different where the nosecone attaches up hidden under the guards.