I've been using Toulene (or Zylene) in both my Grand National Buick (Turbo) and my Buick powered Cobra (11.5:1) compression for several years. Simply mix either at 10-20% (no higher) with a good grade of 93 octane and you get a true 96-98 octane fuel. Its cheap and easy to use. I ALWAYS mix it in a can first though.
Also, commercial octane boosters are a joke. If you could put 12 ounces of ANY chemical in a full tank of gas and get 100 octane the
oil companies would be doing it.
The other alternative is mixing race fuel with 93 octane to get what octane you need. Turbo's need a lot of octane depending on the boost. My Cobra only needs a little over 93 to be "happy".