I don't know how the 62 Galaxies compare with the 64s, but just for a point of reference on my '64 I ran 255/70 R15 tires on 15 X 8.5" Centerlines, with the 4.5" backspacing on the wheels. Those tires are probably the same height as the 275/60 tires you are thinking of, and height wise I had no problems. No problems with the width either, but my tires would be skinnier than a 275/60.