I understand the challenge. Seems wasteful not to be able to adapt an older windlass to your current needs. The S801 was made from 1990 to 2000. It’s been out of production for 25 years.
Perhaps you might find a used unit from a boat salvage yard.
More likely you will need to find a replacement windlass, if you can’t find a machine shop to make one for you.
Perhaps the Lewmar Pro Fish 1000 can be fashioned to fit the space.
he Lewmar Pro-Fish 1000 comes factory-equipped with a gypsy compatible with 8 mm (5/16”) G4 chain.