Hi Rev,
Without a picture, I was going on what you said about it being a 1500. It is a Weedeater XR series engine. I had a small one, many years ago. I replaced it later with a XT-90 of 30cc. Both series have reed valves. The XR on the bottom and the XT in the rear. The flywheel threads are most likey 5/16x24. You will have to enlarge the ports and trim much metal from the case to have usable engine. I would recomend going to a small engine repair shop and picking a good used Homelite or Ryobi for $5 or free. A picture is worh ten thousand words. good luck.

Dave