Neat stuff! I like the little switch guards. I designed a piece of equipment that flew in aircraft (not space) and I used U shaped handles to prevent some lever switches from being thrown accidently. Not as spiffy as some special hardware but it worked; it just didn't have the aerospace 'look'.
I don't know what all the functions of this chrono-gizmo are so I'm just throwing out some chip counts If I had to do this in 1975:
Timebase block:
7 = 1 Hz from 1 MHz needs 6 decade counters & a mux to select input source for clock & timer,
Current time block:
8 = 6 decade counters + 2 logic to preset counters to correct time and handle 24 hours
Countdown timer block:
6 = 4 decade counters + 2 logic to preset counters
Display block:
10 decoder drivers
I/O receivers and transmitters, maybe RS-422?
Switch debouncing
Power supply
This would put the chip count in the mid 30's. If there were special functions like external preloading of values, generation of time code blocks for other equipment, multiple times or mission day count, it could increase the count considerably because of adding muxes or busses. Also, space stuff generally needs rad-hardened chips which may limit the selection. A state machine with a RAM might be interesting, but it may not be available. Even some MSI like a decade counter could be a problem.