14" wheels were standard on full size Pontiacs from the late 1950s through 1968. They went to 15" as standard in 1969.
Board member 61 389-348 just put some 16" eight lug wheels on his 1963 Grand Prix, pictures are in this thread:
http://forums.maxperformanceinc.com/...d.php?t=727684 Scroll down to the bottom of the page.