Vibration issues

I have a nice Navigator which I built up from a box of bits. It went together pretty well, and I couldn't see any reason why it had been stripped down. I spent a large sum re-chroming and repainting and was prepared for the inevitable engine rebuild, but checking play in the big end and piston ring clearance suggested this wasn't necessary. So I put it back together without stripping down the bottom end.Copy and paste link for youtube clip http://www.youtube.com/watch?v=Ib-Otc7aEmwSince then the bike has covered around 100 miles, at a modest pace, never exceeding 55mph for any length of time.I am, however rather concerned by the vibration at high revs.Below 55mph in top gear the bike is relatively smooth, with only a little vibration. However once I push it up towards 60mph the handlebars vibrate so much I am worried I may get white knuckle disease!Is this a common experience or am I likely to have an engine problem that needs investigating? I initially thought that a problem would manifest itself in a catastrophic failure at some point, but it doesn't seem to be getting any worse! I don't really want to strip her down again if I don't have to.I don't expect much from the old girl, but she does seem willing to go above 60mph, it's just that I can't handle it!