The screw you need is 50517-S2, 1/4-20X1/2 pan Phillips, and you also need a nut, 55734-S2, 1/4-20 hex flange serrated base. The screw is only used for the choke cable from 64-67, but you can cut a 50527-S2 screw from 5/8 inch long down to 1/2 inch. It's available at AMK. The nut is used sparingly, convertibles mostly, but also available at AMK. These two hardware items are documented in the Library Section under "Mustang Hardware Spreadsheet 64-66, file MHW64-66AP01.xls. Look under "CARB,CHOKE CABLE BRACKET-DASH . . ".
Jim