I don't know where you are located at, but Motorvation Engineering in Sibley, Iowa can fit a chair to the R3, while you wait.
There are a couple of problems, however. The R3 has a lack of trail and that will require a leading link front fork (Earles type) or a set of re-machined upper and lower trees to increase the rake. The R3 is frameless, that is, the engine is a stressed member of the frame itself and that will necessitate special mounts to be fabricated.
Personally, I think the Watsonian is uglier than a mud fence, but then beauty is in the eye of the beholder.
I've seen a couple of Rocks with tubs attached and n one of them are beauty queens.