I suppose, in a nutshell, you want an Omega 'MV5'/'M5V6' or an AMGega, or an 'RSMV6' then. I suppose that's Eibach springs, Bilstein B6s, and the poly route mentioned already, whatever nice interior bits you like, be it leather Recaros etc. plus Irmscher/Steinmetz bodykits if you wanted. There's been plenty on here done one, or all of these, to good results.
As for the engine, well, one bloke put an engine from a Nissan Skyline, or something, a bit ago, for 400bhp, or something insane, and the chassis handled it, by all accounts. I don't really 'care' about Jap cars, but someone will be able to remember what car it was from/a link to the thread. Very interesting it was too, he did some very nice brake upgrades also. 
I guess you are right with your 'MV5'/'M5V6' or an AMGega analogies. In a nutshell this is what I want. But RS, nope, thank you.

But there is already a 'MV5'/'M5V6' or an AMGega. It's called a Steinmetz Omega. Problem is finding a real one which is not just a normal Omega with a body kit.
As for the engine, I am with you. Not a fan of Japanese cars, so would prefer to keep the engine Opel. If not possible then at least European.

Problem is spending too much on an engine transplant is probably not wise. And if I would, it would have to be for a really substantial gain like 400bhp. Doing an engine swap to get 250-280bhp is not worth it if I can get 230bhp out of the V6 with a remap and some small mods.
And thanks a lot for the "recipe" for a 'MV5'/'M5V6' or an AMGega! Very much appreciated.

So with Eibach springs, Bilstein B6s, and the poly bushings, it would not become too stiff? And how much lower than the MV6 are the Eibach springs? I would rather not have it too low. Cops around here are very annoying about that.