From a few e-mails, it appears I left a thread hanging.
The displaced case volume is of course the engine displacement in a single, or 360° parallel twin, and half the displacement in a 180° twin, etc. (which still has some pumping, but it's between the cylinder mouths below the deck).
A V-twin always has somewhat less than 100% case volume expulsion because the 2 cylinders don't reach BDC together, so the volume displaced is the full piston area × the stroke length at 1/2 of the V angle: 22.5° BBDC for H-D, 45° for Ducati, etc. The exact figure of course depends on the rod ratio.
For a 80" OHV twin (4.25" with 7.4375" rod) the effective stroke at 157.5° ATDC is 4.133" giving about 97% of engine size as volume change.