Hi. If the chainset is an Alivio MC10 then 110mm to 113mm should work. It depends on whether the chainset on now is original to the bike. Have a look at Sheldon Brown's BB sizing table: https://sheldonbrown.com/bbsize.html. I went on the 1994 Bobcat Trail specification as couldn't see one in the 1993 catalogue in the Archive (https://www.retrobike.co.uk/gallery2/v/Manufacturer+Archive/Marin/Catalogues/) but it's a German catalogue so maybe it was available in the UK in 1993 but with a different chainset to that Alivio one? Anyway, see what works with the chainset you've got and all should be well! And, yes, it should be 68mm BB width.