The small pipes coming out the end of the exhaust canisters (piggies) are bent into a vertical stack on the Tourer. And on the Interstate they are in a horizontal position. So, unless you cut off the piggies, I don't think tips from an I/S will fit.
To keep from causing damage to a nice original set of pipes, why don't you get an 18" pair of straight cut tips to put on. It will look much nicer than either Tourer or I/S tips.
Thanks for the info, and the great suggestion.