[NorCam]

It really depends on the car and whether or not it's a car of true significance. For instance, a solid lifter muscle car (i.e. L/78 or Z/28 for example) is always going to be priced above that of a lower horsepower hydraulic flat tappet muscle car (i.e. L48 or L35 etc).

IMO...a true numbers-matching muscle car is going to suffer a 25%-30% hit in value right off the bat. That's due in part to the fact the entire car would need expensive paint and restorative work to bring it back to its original color, should it truly be a car significant enough to save or bring back? It's getting more and more costly for a complete paint job with quality materials, and those guys who do nice work on these older cars are becoming harder and harder to find nowadays.

Now if it's a simple coupe or hotrod car with a swapped engine, trans, and diff...then none of it really matters. Paint it up in whatever style or colors you like and never have another thought about it again.