running a higher octane gas isn't going to give you any more power by itself. All a higher octane rating dose, is it resists detination better then the lower octane fuel. Granted, a higher octane gas will allow you to run more timing, which means more power, but we are talking maybe 5hp, and alot more expensive fuel. I would think that you shouldn't be able to get by on 87, considering that you had the head milled, but if you can once you get the timing dialed in, then dont bother buying expensive gas.