Do you have a set of the 1967 Mustang Assembly Manuals? I see one screw (52052-S13) on page 38 of the body manual for the frame to the track, and a second identical screw used on the vent window itself as shown in the 60-68 Ford Car Parts (aka MPC) Section 230 pg 52. It's described as 6-20 X 1/4 FLH 0.262, XREC, BLUNT TIP. As a chrome plated screw, it was only used on 67 Mustangs, 68 Mustangs used a -S9 finish, bright zinc. As far as I can tell, no other Mustang used this size screw. It is not available at AMK separately, but may be part of a kit.
Jim