I'm running 225-60-14's on the rear of a 66 Valiant, and the wheelwells are much more restrictive than on a 67-69 fish. I ran 60's on my old 68 Cuda coupe, but I don't remember what size - Old Timer's Disease.
There is plenty of room for a 60 series tire. I have 255/60/15s on 8" wide rims with 4.5" backspacing. You might want a little less backspacing if you are going with a 7" wide rim.