picked up my 29ft nordic last summer.the ownes husbend pasted.the motor calls for 92 oc minn.can only get 91oc.dont know what he got at the pump but he mixed berryman oc 8oz to 10 gals.what can this motor handel?

Turn back the timing to 30-32 should be fine with 91.

and get rid of the oc add? can this motor handle 100oc ?

I would get rid of the additive,they don't really work.
Why would you want to run 100 octane? Not needed