Oh, please don't do it. Keep the tubulars. Even cheap sewups ride *so* nice. I was intimidated by them until I took the plunge with my Pro, and I am now a convert.

Vittoria makes a perfectly acceptable tubular tire that retails for about $40, has an anti-puncture layer, and rides like buttah. Seriously, before you go to the expense of a wheel build, don't you think it's worth at least trying them out? If you find it's not for you, then sell the gear on down the road.