I've had a cap on my dash for over six years now, and no one has even noticed. From the outside it looks normal, if you open a door, you can just barely see the original pad sticking out about 1/4 inch. No biggie. If your's is green, I would trial fit it first and see what sticks out and then shoot that with black vinyl dye so that it isn't obvious.
I will keep the 74 dash pad for the 69 notchback cuda thats going to be next on the rotisserie. I will prob put a cap on that one.