I would reach out to Sonosax to find out more as your head unit is marked as Mono (and for aligned for a specific type of tape) and not stereo so you may want to find out what that means (i.e. is it a playback only head, does it record 2 channels of mono, does it reocrd 1 channel mono, etc). They should be able to help out how the unit is configured - which in turn would help you figure out value.
Decks with mono heads are typically worth less then decks with Stereo heads
FWIW - where ever you found this you may want to see if the have any more parts (heads, cables, internal modules, reel adapters, etc)