I would restore it to factory look on the outside and interior and upgrade the suspension and drivetrain. Since the Olds diesel was already swapped out for the Olds gas (very common back in the day, since the Olds 350 diesel was a terrible mistake!), I would build the 403 for more torque, add an overdrive trans and some deeper rear gears. Make it look like an old man cruiser and go like a musclecar!
Steve

nice ride.  Since the original engine is gone, a numbers mathcing resto is pretty much out.  If it was mine I would give it a lowered limo-like look.  Dark slate grey with dark tinted windows, a little lowered with chrome 18 inch wire wheels and all the chrome trim available.  kind of like the VIP import car theme but with a real american car instead of a high end import.
A friend of mine got a 1979 parisienne 2 door just like your bonnie from his dad when we were younger.  Man did we enjoy cruising around in it.  
Welcome to the group
Dean

Right now it has (I think) an Olds 403.  It was originally a diesel, but my dad told me he went through some deep water and killed it a long time ago and he swapped it with the Olds.

Welcome to HPP! Great to have you here.
I would vote to restore it to original but its your car and its great it's being saved either way!
What engine does it have?
Take Care,  Pete

Thanks

Welcome aboard.