If they have a side-rail for flash, you want a Flash Unit Y. This has a built-in delay relay, and takes bayonet base flashbulbs. The earlier side-rail units were Edison base, although the bayonet converter is often with them.
There's really a lot of subtly different models and accessories. Not common, but not many collectors.
If it's a battery-capacitor unit, expect the capacitor to be kaput.