1. Looks like it depends on whether or not a clock is installed.
No clock - you're good from 73 - 87 (up to 91 for Blazer, Suburban, etc):
(1973-87) Instrument Cluster Face-w/ Gauges w/o Clock
With a clock - for some reason, 80 and down is different than 81 and up:
(1973-80) Instrument...