Will they fit my 64 Dart GT?

I have found a set of 15x7 inch rally sbp, with 4.25 backspacing. They have P 195 65 r 15s firestone affinity tires like new. They came off a 71 duster with standard drum brakes. They look small enough, but the 13s on it look tiny, with tons of extrs room. Does anyone know if they will fit my 1964 GT convertible V8. small bolt pattern.
h2ojoe