I know what you mean by do it once but unless you build and then quickly sell it the changes will keep coming. My 1903 build started in May and I consider it done(ish) now although there's a few parts on the bench waiting. Done, but not really. I wanted it on the road so I could have some fun and I wanted to get going on a fairly basic build so I went two stroke, KW mounts, etc. The "plan" is swap out the engine next year after I sort out a drive train on the bench. Until then, I can ride and wrench too! There are a lot of nice 1903 builds on the forum, plus the Phantom Ghost that was mentioned. Also take a look at the Ridley 1903 for ideas.
I like my ride as is but the next drive train needs to be something a little different. That's just me though. Good luck on the build and great score on the bike! They don't make that model anymore.