As you mentioned, the most difficult part of this particular build with these two 67 Coronets would be the repaint of the Black R/T's hood and WO23 hood scoop assembly to match the Blue Campbell's car and even if you found an aftermarker WO23 hood scoop, you'd have the same problem.
As far as the interior and chassis swap from the Black R/T to the Blue Campbell's body goes, that shouldn't be that difficult if you're really careful, as other than having to do a wheel and tire swap between the two cars, the complete interior and the rest of the Black R/T's chassis assembly with it's 440 engine and 4 speed transmission would be a direct swap.
As with the Blue Campbell's car though, the Black R/T is also a Limited Edition model with only 1002 being produced, so modifying one of those for some would be a difficult choice.
So folks know what the Black R/T looks like, here's all of the information on it and a picture.
Manufacture: Diecast Promotions aka Highway 61
Produced for: Supercar Collectibles as a Limited Edition release
Series: Super Street series
Release date: December 2004
Stock / Item number: 50285
Number produced: 1002
Suggested retail price in 2004: $64.95
Model: 1967 Dodge Coronet R/T
Color: Black, Black interior
Engine: 440
Transmission: 4 speed
Wheels and tires: Cragar mags with black wall performance tires, cheater slicks on the rear
Working features: Opening hood, doors and trunk lid, steerable front wheels
Richard