I did a build for my wifes bike similar to what you did minus the customization you had to do. I used a Cro Mo clearance Performance frame which was surprisingly light with old XT/XTR parts laying around and some old Sun rims with Ringle hubs. The bike turned out to be pretty light and very quick and she definitely noticed the difference from the clunker she had been riding.Conclusion: I took it around the block. Shifts are tight and crisp, the Avid SD7s are just like their namesake, 'single digit' braking, the MX Pro ETA is buttery and almost old school Cadillac like. I felt like I was floating around the block. Acceleration is ridiculous, I attribute this partially to the length of the beach cruiser handlebars and mainly to the thirteen year old wheelset.
AND, it is tough to believe, but weight without pedals is 23.1 lbs! WTF! I am reluctant to let my wife ride this and question whether or not she will appreciate the amount of research, thought, and work that actually went into pulling this off. I love her to death, but wonder if there would be any difference to her between this bike and some Target special. My only solace is that I built this for her to 'ride', not to 'have'. Petty, I know, but it keeps me sane!