sounds like a big money project, very interesting idea
you'd need a different chassis and the hardtop wont fit anymore. it would deffinitely be something different!
but i would not recommend cutting then welding the original frame.
alternatively you can get the roadster hood, that would eliminate the rear seat, or even an over grown speaker box to sit on the rear seats
i think some of the appeal of the capri is that it looks long without being physically long (especially after lowering it). but thats not saying that it would not look good otherwise
tell us how it goes