Does anyone know what the backspacing on the 15x7 AMC rally wheels used on '71-'74 Javelin's was?

I want to put a set of 15x7 wheels on my '73 Javelin (currently has the 14" rally wheels). It would appear that any backspacing from about 3.75" to 4.5" would work. However, I would like to know what the factory 15x7 wheel was for a reference.