I've seen several Streets modified into a pure dirt bike configuration. Typically the first thing is to change from a belt drive to a chain drive (belts are better for the street and chains are better for dirt) and along with changing the springs, shocks and tires, offing the fairing, and a few other mods you have a great dirt bike. Might also switch to spoke wheels and tubes for repair purposes (which is why a chain is preferred over a belt).I watched Avengers: Age of Ultron last night. Captain America was riding a 750 like a dirt bike through the forest, I dont think that would work. Still pretty cool though to see Cap on the Street again.
Note: I might also move the foot pegs slightly forward an inch or two because you spend most of your time on the pegs in the dirt. Where they go exactly is based upon "balance" and so I don't know exactly where I put them.