For 1968, the clock was available from the factory in three flavors:
1. Part of the RPO U17 "Special Instrumentation" package
2. RPO U35 (which required the RPO D55 Console)
3. Part of the Group 4 "Operating Convenience Group", which consisted of other additional options as a package:
a. Early 1968 Convertible: Included RPO U35 (Clock) and RPO D33 (Remote outside rear view mirror)
b. 1968 Coupe: Included RPO U35 (Clock), RPO C50 (Rear defroster) and RPO D33 (Remote outside rear view mirror)
c. Late 1968 Convertible: Included RPO U35 (Clock), RPO C50 (Rear defroster) and RPO D33 (Remote outside rear view mirror)
If the U17 (Special Instrumentation) option was ordered, the clock came in the tachometer (Tic-Toc-Tack).
If the clock was ordered as just RPO U35, it required the RPO D55 console and was mounted on the console.
If the Group 4 "Operating Convenience Group" was ordered, the clock was mounted on the floor.
Note that although the part numbers are different, the clock (mounted on the console as P/N 3921410) and the clock (mounted on the floor as P/N 987185) was the same. Only the trim pieces were different. So basically there were really, only two different "clocks". The clock in the tachometer, and the clock mounted on either the console or on the floor.
And of course, it was also available as a "dealer installed accessory".
Ed
