I really think you have to let this one go.
But since you will strip the car anyway, then you can start by taking the doors off. Take the seats out. Remove the carpet and headliner and interior mouldings, so you can see the shell.
From all the custom workshop vids I have seen, you will do something like..
Cover up (protect) the centre tunnel where the gear lever is. Also cover the dash and cluster and steering wheel.
Now you can see what you have to work with.
Take measurements around b pillar and compare with the other side of the car. See how much you have to adjust.
The shell (roof to floor) has to be braced by tack welding rebar before you cut the b pillar out. Then cut it out and cut an identical straight section from another shell. Make adjustments to your shell to fit the new b pillar in place.
I suspect that you will give up before this point or you might get the b pillar tacked inplace and find the doors don't fit.
So just keep stripping the car and use those parts to fix up another Commodore, well you tried and did what was best.
Measure twice and cut once.