That is a very nice looking bike, it should make for a pretty easy and good looking build.
I ran into a similar issue with mounting a China Girl on my Schwinn. I went with a welded front mount, made from the mounting flange provided with the kit and an old piece of 1" seatpost. A local muffler shop welded it together for me for $20. I have a thread on it here: Cost to weld front motor mount?