I still do them. I ocassionally build an engine for sale, or do one to order for a past customer. I don't generally do parts for sale though, as I don't have the time and energy, plus there is just no way it is worthwhile. By the time you hand craft individual pieces for a conversion, you can't charge anywhere near what they are worth. That's one of the reasons nobody makes the conversion parts any more.
The influx of cheap Chinese engines has all but killed engine conversions, though I personally still feel they are definitely worthwhile as you get the satisfaction of creating something yourself, but more importantly, you get a much better engine.
At the moment I have a Poulan Pro 42cc in the works, and a real nice Kawasaki 50cc. They will be for sale, but progress on them was held up due to a fairly recent back surgery.
AV8TOR