The headset stack height means that once it's installed it will, in effect, add 28.8mm (usually has an upper and lower for both parts of the headset) to the length of the head tube, and the stem stack is the measurement from the top to bottom of the clamp at the steerer tube of the forks.
Cheers mate. I'll be getting the debit card out then!
Cheers mate. I'll be getting the debit card out then!