Starting in 72, Chrysler standardized the side marker lights across the board as a cost savings measure. Challengers, Cudas, Chargers, Darts exc...all used the same side markers. If Roseville sells one for a Challenger, it should fit a Cuda. I've seen the flush mount 72+ side markers done only once. I really like it. Personally, I don't like the look of shaved side markers on these cars. It just seems like the easy way out.
You could graft on the 70-71 style side marker. If the car needs fenders and quarters anyway, just put 1970 parts on it. There is a member on here who put 71 Roadrunner(three piece) side markers on his Challenger. It really looked cool...so much nicer then shaving the lights.
But, at the end of the day, it's your car. You can do what you want to it.