the max volume is easy to figure out... unscrew the shaft, fill it w. oil, screw it back together and remove the schrader valve... position the shock so that the schrader is your "bleed" point, highest point... now hook a tube to the schrader to prevent mess... fully compress the shock, the shaft diplaces the fluid and the amount that is left over is the max amount of oil...
now take the shock back apart, carefully as to not spill any oil... then measure the oil w/ a large syringe... there you have it, maximum ****in oil capacity...
i buy my syringes at a farm supply store, they are a buck a piece and i get the 60cc ones... grind the end smooth and you can use it to stick in the schrader valve to add oil.. add this w/ the cheap nitrogen valve and you have a cheap air shock tuning kit the CCE way....