which apparently has no engine alarms (horns.buzzers, etc), just gauges.
Apparently? I have a 1986 C34 which has the same engine cockpit panels that Catalina used for many years before that, and we have alarms.
Regardless of whether the contention that they didn't have alarms is true, which i doubt, or whether they did, is immaterial.
What your friend should do is open up the panel. What he'll most likely find is the small alarms, which were "notoriously"
underpowered to be able to hear when the engine was running.
They are most likely actually there, but either broken or the wiring is toast (at either end).
What engine does the boat have (A4 or M25 or 5411)?
Seaward, who still makes panels and replacements, has the newer, louder buzzers.
Only by opening the panel up and looking will you know.
I'd be truly surprised if there were no alarms there.