I hate to be the one to burst your bubble, but there is no 1964 Mustang
, only the 65...the early production (April to Aug 64) are called 64 1/2's.. to tell if it is one, it has to have a engine code of one of these..D,F or U .. that's the last letter before the unit number.. I would shy away from a U code, you can spot them by their 4 lug wheels, they originally came with a 170 ci inline 6, but odds are it's been replace long ago. the problem with them is their small brakes, no good for stopping, so unless you are doing a complete resto rod with new everything don't go there..
and like the others have said, watch out for rust, especially in the subframe assemblies.. also make sure the dataplate on the door matches the vin on the top of the drivers fender...learn how to decode by printing out a vin decoder, there's one in the links of the group below..