It,s mainly mechanical parts that I am after, such as, brakes, suspension, exhaust manifolds(or headers as they call them) and systems but with the different wdith, I am assuming that the floor plan is different? Also I am unable to find a 3.0l listing in the Commodore range...?
Never heard of the different width thing, before, to be honest. You should be very well catered for, as I said, with the oily bits, though. The PCD is different, that aside I've heard of Holden suspension fitted to Omegas.
There's a lot of disagreement about this, so here's my attempt at straightening it all out (Deep breath...) For anyone that doesn't already know cars are VERY expensive things to develop, (200million just to FACELIFT the Omega in '99) and so a car often shares what's called a 'platform'. This often includes floorpan, scuttle and suspension, drivetrain too. Over-simplification often re-terms this as a 'chassis', or 'floorplan'. This is, as with a lot of things sort-of right, sort-of wrong. But a good example is the Astra and Zafira. They look pretty different cars, but do share the same platform. To say they are 'the same car with a different body' Yes, it is TECHNICALLY incorrect to say this, there are no doubt loads of boltholes, pressings, flanges, blah blah blah that will be different, but one heavily borrows from another. Yes, there are differences, but they're BASICALLY the same. It happens SO much more than you'd think - Didn't know that under the skin the first Discovery is basically an old Range Rover, did you? Aston DB7 / Jag XJ-S, Morris Minor / Marina, Mazda 3 / Focus, Jag X-Type / Mondeo the list is endless!
The Holden Commodore VT / VX / VY / VZ share the same platform as the Omega. So when people say 'No, no its not the same car, look at the front end, look at the interior, etc..' they're half right, half wrong. Just as those that say 'They're the same car, different badge' again, half right, half wrong.
It is therefore totally feasible to take the front end from a Monaro, and bolt it to the mid-section of a Opel Omega, to the rear of a Cadillac Catera. Three cars, three continents, but all share the V-Car platform, that goes right back to 1978. There's a guy on oof that's just put an old 1980s 2.3TD Carlton lump (with a Monza 'box) in a Facelift Omega, it drops pretty much straight in!
Wikepedia does a decent job of explaining the Omega platform thing -
http://en.wikipedia.org/wiki/Holden_Commodore#VS_.281995.E2.80.931997.29Hope that helps!