Cal 2-29 Re. Starter replacement

I've owned my Cal 2-29 for fifteen years now, it is a 1974, and it is finally time to replace the starter on the Farymann 12hp diesel engine. I removed the top nut from the bolt but cannot seem to remove the bottom nut from the bolt. Is there a trick to removing the nut to remove the starter without pulling the engine? Any information would be of great assistance! Thank you in advance.