My 67 GTX has the same deal, and so does my 67 Coronet. I have posted on here about it before, but no good response. The outlet nipple for the return hose on the pump is 5/8, but the steering box valve is 3/8. I wound up using brass fittings to reduce it. I saw a magazine photo of a 66 Sattelite with a plastic reducer fitting with the correct hog-ring style clamps. There must have been some kind of reducer, but you are the only other person I have seen post about it. I need one too !