since your post is 10 days or so old, and no one replied, thought I would weigh in....and you well may have fixed by now. That is tough job, changing that belt on Onan DKD. Just did one last week and took me couple hours, and I work on those things for a living.
You have to get the fan/belt guard off to access the alternator bolts to
loosen it. You may have to unbolt mount bolts and partially slide set out of compartment to get the guards off. Belt should be available at any auto parts store, or Onan or Kubota dealer (engine is a Kubota) Good luck!
