well, i don't have experience with your forks specifically so i can't say. but unless someone else has a better method to offer or you can't find out in the literature then i would suggest you loosen the fork caps, remove the forks, remove the caps, carefully remove the springs (keep them clean), collapse the fork and measure the oil level from the top of the fork tube. without better info, this should get you in the ball park. you may also want to drain the oil into a container then meaure the original amount so you have an idea of the quantity required. again this in case you can't find the fill volume listed somewhere. good luck.
i would stay with the oil weight listed for the forks in the manual unless your planning to revalve to some spec that requires different viscosity.
"Life is too short to do anything other than that about which you are absolutely passionate."..........."Adventure is a frame of mind, set upon by action, not defined by equipment."..........."I didn't get a Sportster because I wanted a Harley....I got a Harley because I wanted a Sportster."..............."It all boils down to your ability to say "SCREW IT" and really mean it".....Randy