Understood

These are a nice easy way to see how the rear suspension fits together, and also any differences between the saloon and estate

you'll also see from the Monaro pages that the only significant difference is that the diff bolts directly to the subframe, but the rear diff mount is identical to the Omega...
This is good for two reasons, 1. A Monaro rollbar, (stock or uprated), should fit nicely, and 2. Any pics that Pete can send you will be of use because there is actually very little difference between the Omega Saloon and the Monaro rear set up

I suspect that what Pete has fitted to his Monaro is as follows:
Front, actual coilovers, like your green example, as a direct replacement for the stock struts.
Rear, lowered springs with adjustable seats and adjustable dampers, each being straight swaps for what is fitted to the car.
As I understand it, you are intending to fit complete coilover units, like the front ones, to the rear

This should be doable, but you'll likely need to strip the boot out and cut out the inner wings and rebuild them to make the top mounts. This would be less work on a saloon, but you've much better access on the estate

(suspect fuel filler will be in the way though). You might get away with a bracket up in the wheel wells but could be some horrendous clearance issues
If you try to use the existing shock mounts in the floor, then you're into cutting up the chassis rails to create the top mounts. Again doable but will the coilovers work properly at such an angle? About 60 degrees rather than vertical.
I'd be sitting down with 2woody and Master DTM to sort out the finer points of what you're trying to achieve
