[Lanny]

While Ford did come out with a 4 1/4" bolt circle on some models a
few years ago, Your 9" rear and Mustang 5 lug front should be 4 1/2".
Measure using the chart that dmsfrr provided for measuring 5 lugs.

Also, you say the center hole on your 9" rear is different then the wheels
you are using. Is that center hole smaller then your wheel center hole ?
I believe it was in '69 that Ford changed the size of the center hole.
Ford changed from 2 3/8" center to 2 3/4" center hole.




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