Capri was light as a feather compared to an Omega though. One Omega front seat probably weighs as much as a complete Capri interior.
I agree about trying to turn a big heavy comfy barge into a track / fast road car though.
Its a bit like the old Irish joke "can you tell me the way to Dublin please ?"
"Well, I wouldnt start from here."
However, if someone really wants to do it, shedding weight would be the best way to go imo.
Not just for straight line performance, but also for braking & cornering.
Only by removing structure, and the Omega doesn't have much of that to begin with, GM preferring to use less, thicker gauge steel than adding reinforcement.
The Barge weighs the same as an Omega but has significantly more metal behind the scenes.
Incidentally, the car in question is a Scimitar, so isn't exactly over weight... The 3.2 should already be a significant upgrade from an Essex V6.
An LS1 with a cam would be nearly twice the output of a 3.2
And about the same price as getting another 30bhp from the 3.2