I have also heard of a conversion kit,  but it was long ago when they stopped selling 3 wheelers.  Not sure how good they were, and bet it wouldn't be cheap or easy to make it work right.  Only 200 miles? Thats amazing, and I bet you could sell that thing for a decent price if you decided to in order to buy a 4 wheeler.  Those sure were popular back in their day and I still see a few in the beds of pickup trucks these days.
markc :-)