The numbers on paper look good...I am 6'4" with a 38" inseam so looking for a somewhat short bike (~60cm TT) and as tall as headtube as possible. Anyone know if the 23.6cm head tube includes the bottom and top cups or what the length is from the bottom of the headtube to the bottom of a stem with maximum allowable spacers?

I am 6'4" and ride a 62" steel/carbon Fierte with no problems. I wouldn't characterize it as a 'short' bike though. I believe the head tube is without the cups and do not know the measurement from the bottom of the cup to the stem.

The Serotta head tube measurements are done without the headset installed.

The amount of allowable spacers is dependent on which fork is used, the fork manufacturers determine that. For instance Reynolds states that max allowable spacers for their 1 1/8" fork is 40MM (1.58"). Add that number to the stack height of the top portion of the headset and the head tube length to get the distance number you want.