I think it is really unlikely that a 23.5in frame will have the same geometry as the 21.5in whose geometry is listed. The larger frame is likely to have a shallower seat tube angle and maybe a slightly steeper head angle - the only real way to find out what your frame's geometry is, is to measure it. Making a half scale or ideally a full scale drawing of the frame will help to ensure you get it it accurate as measuring frame angles with a protractor in incredibly difficult. However by doing a drawing you can see if what you measured actually all adds up. Altenatively a local framebuilder could check it on his jig...

Hilary