I currently own an 81 Claud Butler Italia with 531 main tubes. I like the bike, but it does seem flexy to me.I get brake rub on the fork and it feels "muddy" when I crank up a hill. I am 6'0", 180 lbs, and the frame is something like a 58cm. I am wondering if the large size of the frame and my non-European body sizing has something to do with it.

I have a line on a Trek 560, 501 main tube, 61cm bike. I THINK the fit would work well. I am running a decent amount of seat post on the Claud. I am wondering is this would be better in the stiffness department. That and I have always loved the look of old Treks.