The reason Heidts say 63-65 is because it's 5 lug and not 4. I used 6 cyl suspension for 25 years with a V8 with no problem. I do like the feel of the 63 V8 suspension I have now. Are you sure your idler arm is in good condition? All Mustang parts will swap except the centerlink...It's too wide. Don't be thinking you can cut a section out and weld it back up. The centerlink is heat treated and if you weld it the heat will make the part weak and brittle. It's true a professional welder be able to do this but getting centerlink from a 65 Falcon will be cheaper in the long run.

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Jeff in Georgia
60 Tudor Falcon V8
64 Falcon Wagon V8