Hello again to all...I noticed a 70s Masi on ebay in my size recently and found that the top tube (described as dented) was really caved in and need replacement. I have had a seatube replaced back in the 80s and understand the simplicity of the approach, but I was curious on exactly how a frame builder would take the frame apart to replace the top tube only. Patrick Lay, geometrically befuddled in Chicago