With all the federal requirements to make a vehicle street legal, I really doubt there is any way that it is street legal. In fact, I would say he is cruisin for a traffic ticket ...
Anything can be made street legal if it fits in a category (motorcycle in this case), is built with all the required items, and is properly titled, insured and registered. It doesn’t matter what engine it has, that only applies to vehicle manufactures that are producing new vehicles.