I agree with ws's suggestion of a thicker walled TT. Not just for dent resistance. I've long time felt that a frame feels best with somewhat balanced tube walls. A single step different (as is common with a TT being .1mm thinner walls often) sure. But two or three steps thinner seems out of step to me.
Consider allowing for more then typical (for intended use) tire clearances as a really tall or big rider needs more air between the rim and road.
Back in my Cyclery North time I built one of the 72 and 74cm frames we did that year. I wish I had the knowledge then that I have now. The frames would have been quite different. Here's a shot of the one I made. Andy
