What you need to compare from a vertical standpoint, is the total head tube length, with the headset, on your Lemond to the total length, with the headset, on a proposed new frame. There can still be some error due to difference in fork length, but it's about the best that can be done, until all brands adopt and report the stack height (vertical) defintion. From a horizontal standpoint, you compare the TT length, but corrections will be needed if the seat tube angles are different. A new frame that has a steeper STA will have more reach - about 1cm per degree.

Frame size numbers are meaningless, particularly with some of the same "size" and same brand having a 20mm difference in the head tube length, depending on whether the frame is a racing model or more comfort oriented model.