Re: head tube replace
Sound like it'll work to me. Just make sure you have good welds since that's such a critical spot for stress. I think you'll find that you'll have to bang the stock 1" head tube out more than you think though. It's narrower than the 1-1/8" head tube by more than just 1/8", so be prepared for some extra massaging of the metal.
Post some pics of the progress, please. I love seeing ideas come to life.