dyno in 4th. You want as close to 1:1 ratio as you can get. Anything else will skew results unless the dyno operator knows the correction factor.
Just watch the AFR. If it goes lean, STOP. Find out why it's lean, fix it and then continue to dyno.
No. Do not use any type of Octane booster. Dyno on the fuel you normally use, nothing else or foreign.