In the first place there was no such thing as a V6 in '65. If the car has a V6 it's something a previous owner did. The '65s had either an I-6 or various versions of the venerable 289 V8. The '65 is an easy car to work on and can be driven while a lot of the work is being done. For restoration parts try http://www.texasmustang.com
Both carry a lot of reproduction parts and parts made from original Ford molds which are sanctioned by Ford Motor Co. The reproducton parts are cheaper but, especially for body parts, the Ford parts fit much better.
Edited: The first purchase you should make from one of those Mustang parts houses is a copy of the Ford Shop Manual. It will provide you all the specs and detailed drawings and instructions for disassembly, repair and reassembly of any part of the car from the engine to wiring to windows, door latches, etc.