What are the possibilities of converting a Tourer model to an Interstate model? Do the fairing parts match up or would it be a little expensive to do.
What parts of the Interstate are you wanting?
If you're wanting a fairing with radio and speakers, it would be much easier to put a Woodys fairing on your bike.
If you're wanting the Interstate fairing, radiator pods, tank and hard bags, it would be much cheaper and easier to just buy an Interstate and take the trunk off.
Just putting an I/S fairing on your tourer is fairly complicated, not to mention the wiring and wiring harness issues that you're gonna run into.
It's not that it can't be done, but it's not a direct swap if that's what you're asking.