When I stripped my '51 SQ4 BA gearbox, similarly unused for an estimated 50 yrs or so, I took photos to help me reassemble it.
This particular photo shows my kickstart ratchet freshly removed from the end of the mainshaft, i.e, opposite end to the clutch, right in the middle of this photo.
If yours is a BA box, My guess is your toothed ratchet is is not free-running, i.e has become locked together either "ratchet-face to ratchet-face" or maybe via the steel bush at its center. (You can see this bush still on the mainshaft just below and to the right of the ratchet spring in the photo.
Maybe it is bound by either rust or solidified old tallow style grease perhaps? Regards, Brian.