Hi John,
I understand. The cooling system, although it works fine, seems to have room for improvement.
I got my expansion tank from MSI motorsports a couple of years ago. It is fine, but they are making some more attractive units now - check with Woody. They are just the right size for a se7en. If I convert my system at some point in the future, I'll get a new tank from them.
Regarding the SBD water rail, I was asking myself the same thing: "where does the coil pack go?". I suspect you are right and they use the coil on plug setup. Either that, or you have to fashion some kind of bracket for the coil pack.