I don't know if anyone else can see the images in the Torviki thread linked above, for me they just show up as "Posted Image" text. However the images are still there, click on them and you can see them in Photobucket (twice...). I'll have a go at re-posting below and see if they show up.
The cast iron LH / early LX calipers are a reasonable caliper but they are fixed in width so you can't use them on the thicker vented rotors.
The late LX / early UC calipers are the bolt together two piece aluminium with cast iron carrier, these are the horrible calipers. HX and early HZ had the same style caliper with a few minor differences in the main body as mentioned, and a wider bolt-on carrier to suit the thicker vented disc. This is the easy changeover option, but I can attest to their poor performance compared to others as datto so eloquently put it.
(you can see the 'Torana' on the pad carrier piece, full sized ones say 'Holden')
The late UC aluminium ones are similar to the late HZ and WB and I don't think too bad a caliper but again fixed in width so can't run the thicker vented disc.
The cast iron HQ calipers datto recommended are a bit heavier but they're quite ridgid so they perform well and relatively small packaging helps with clearance too.