HI Doug,
I would really reconsider Will's advice.. In my experience, Riv bikes ride big.. the Bleriot Grant put me on back in the day always felt too large and the AHH I got from my Dad doesn't feel any too large (with drop bars) for me.. I say that as it should have been sized for my Dad and he was a good 2" shorter than me.. at 5'9" (31" PBH and 68cm seat height normally), I wouldn't consider anything larger than a 50cm and I don't think that will feel small by any means..
BTW- anyone have a 50cm Roadini they want to move on? :)
Chris