Correct for any '68 (and other) C4 or C6 Mustang with standard interior. IIRC on deluxe interior it was vinyl wrapped.
Repro buttons are available, good quality and pretty cheap. The missing one just slips in the end as is held in place by a slot that goes over the shifter stem, probaly fell out of the box long ago...
The lockout and linkage is on the shifter stem.