Higher octane only gives you more performance on engines that were designed for it. If your engine has a knock sensor that retards the timing when it detects knock then a high octane fuel will give you better performance because the ignition can be run advanced and give you more torque. An engine without a knock sensor will actually see slightly reduced fuel economy, emissions, and power because the ignition is set up for regular fuel and the extra goodness is going right out the tailpipe because the higher octane hydrocarbons are only partially burned. If you use high octane and recurve your ignition for it you will get better performance. High octane unleaded was not readily available in 1978 so your engine would be fine on regular.
1955 Willys CJ5 Buick 225 V6 160HP 270ft-lbs, T90 trans, Warn OD, PTO winch, Spicer 18 T Case, RS9000's, Dana 25F/ 44R,
5.38:1 gears, 11" brakes, Bestop Supertop, Hurculiner