Johnny,
There are a few ST's with sidecars attached but not too many. It is a challenging job as they don't have any frame under the engine, so attachment points have to be made up, and all the plastic gets in the way. But if you are interested Sean Kelly (at SRK Engineering) did mine and knows how to make it all work. He also built the leading link front end, which is, as tj noted, very strong. Necessary to cope with the stresses generated by the weight of the outfit and also to change the geometry of the front end and make the steering manageable.
Woffo