From the Mid America Motorworks website:
Tech Tip: Some customers have called us asking "How do I remove my 1963-1967 Corvette Clock from the dash in order to restore it?" It's simple, if you know the trick! Midyear clocks are held in place with two "grasshopper" clips on the inside of the dash. First, remove your center dash lower vent side panels. This will allow access to the rear of the clock. On the back of the clock, you will feel the two v-shaped, "grasshopper" clips. Press down on the open end of the clips and slide them off of the clock ball-studs and the clock may be pulled out of the face of the dash. Re-installation is just the reverse.​