Yes. Its interesting how different folk's ideas/perspective sometimes leads to a real headslapper moment(as in "why didn't I think of that?"). Thanks for the perspective. My 14yr old nephew is looking for his first road bike(new to him but used), and although most used bikes are close to square numbers I will now definitely keep top tube length as a very important variable.I was just going to go with st length and make the tt length work by changing stem lengths, but I'll(we'll) be looking a little more critically at the tt now.
BTW, I'm excited to work with him on this project, his parents are very supportive but non-cyclists, and he thinks its a great idea to work/build up a used bike with his uncle.

Brian