These 3 were nice assembly line ones removed from two 1970 Cuda 340 cars in Dobbins yard in NY in about 1973.
They have the single hole like my NOS one.
On the one verses two holes it was probably a case of different suppliers.
If you notice, Davids NOS hanger has no hole.
On Daves Challenger he used two NOS resonator hangers that I took for him to Carlisle as he was in the process of doing the car.