That does seem kind of a small gap. The clutch probably needs adjusting, and it's not too hard to do. 

Turn to page 6-36 of the Oliver service manual, and it goes over adjusting the release levers. What you'll end up doing is placing key stock in place of the clutch disc so that you can get an accurate measurement to the flywheel from the release levers. It tells in the book how to adjust the levers by turning the nuts on the clutch cover, and also the correct dimensions for the different clutches that were available. Looks like they all used the same finger height except the 66.

Once it is adjusted correctly, you probably find that took care of the small gap.