OK. These are a few bits. But hardly any complete conversion kit. Looks like a lot to chase for 68bhp extra. Not to mention the prices. 
And I would still be interested in reading your reasoning as to why the GSi is twice the car the Omega is. 
If I have to spell it out...
Those parts are merely examples of performance upgrades for the C30E lumps... The Omega A is lighter... The engine has proper tuning potential unlike the V6 which would melt at the thought of forced induction...
And if you click the last link, your car search is over 
You don't need to spell
that out.

We are on the same page about that.

I just don't see how that makes a Carlton GSi twice the car the Omega will be.
Even if it was twice as fast, in a straight line, it wouldn't necessarily be twice the car. A car is so much more than just speed.

But the GSi is barely faster than the MV6. It reaches 60mp/h in 7.6 secs vs 8.0 with the MV6 but has pretty much the same top speed.
This is of course in stock form. Sure, if tuned with the Irmscher 4.0 it gets you an extra 10mp/h in top speed. At least the Irmscher built 4.0 car was 10mp/h faster than the standard GSi. This is not a whole lot. Specially when you consider how much witch hunting you would have to do to find all the needed parts for the 4.0 conversion. It's not like you can just walk in a store and buy.

And like I said, a car is so much more than just speed. There are so many slower cars I would rather drive than faster ones because they are more fun or are better cars in a whole.
It may take years till you can find all the parts to complete the engine. And at over a thousand quid for a crankshaft, not worth it in my opinion.
About the old Rekord Estate ending my car search, I would need to get my head around driving an old 1993 Carlton as a daily. I would not want to drive an early 80's Opel around, Irmscher or not. So that is not for me.

If motor size and bhp was all I was looking for I would just go the old American V8 muscle car path.

I need a car which is also practical. Not only a weekend car to toy around.

Put another way, that's 68bhp more than you'll get from an X30/Z32 lump in a car that is lighter 
Sure. But it's lighter for a reason. It's lacking every safety feature on the book. I think the only modern safety feature it has is ABS. Chassis stiffness is also worse than the Omega. Probably part of the reason it is lighter. It is also much more prone to rust. Old tech. Most likely harder to find parts than for the Omega etc. That is all even before starting to discuss things like handling, which matters more than just speed. Or before analyzing if the Carlton is as reliable as the Omega, address electrical problems and other things older cars are worse at.
So I'm still not seeing twice the car there. Sorry. This is the part I would need you to spell out for me.
