The '64-down ring-style shroud bolts to the radiator support panel. The '65-up box-style shroud attaches to the radiator with four brackets that require correctly-located slots and captive nuts. As far as I know,
no mass-produced aftermarket radiator is configured to accept the box-style shroud. I am reasonably certain that
this guy can make you a radiator that will accept the shroud, if you send him your original radiator with shroud and brackets; contact him and ask.