I though you all might be interested in this info as many of us have the AP and Baader BBHS and Zeiss spec prism diagonals (with the T2 quick changer system).
Using my DPAC test set up, I directly measured some interesting stuff.
1. AP diagonal has a 105mm light path from the front face to the top of the diagonal.
2. The Baader BBHS silver diagonal has a light path of 51mm from the front face to the diagonal to the top of the T2 quick changer
3. The Baader Zeiss spec prism diagonal has a light path of 39mm from the front face of the diagonal to the top of the T2 quick changer.
4. With the 1.25X and 1.7x GPCs screwed into the bottom of my Zeiss 30mm CA viewer, I needed to rack the focuser out an additional 21.2mm and 38.8mm respectively, on average, for all three diagonals.
Regarding number 4, when you reverse the GPC elements and put them into the quick changers rather than into the bottom of the viewer as I did, those differences in focuser rack out will be slightly larger, maybe a couple of mm's, as they are slightly further away from the focal plane in that configuration, giving them slightly more magnification.