I'm not sure about the octane rating as far as where fuel is sold, but the volatility is different. Fuel formulated for higher altitudes is designed to be more volitile and combust more readily and more rapidly, whether it's more or less resistant to detonation I'm not sure, but I imagine if it's more volitile it has less detonation resistance. They do that to help make up for power lostfrom reduced combustion due to the thinner air.As far as that 98 octane, you'll be fine on 87 or 89. I was running 89 in my 302 and it has a helluva lot more power than a stock 289/302, the only reason I switched to 91 was that I had a part throttle detonation problem, but if I put some effort into it I could tune that out via ignition/carburetion. With 98/100 octane you could run 11.5:1 compression or a crapload of boost, so unless you have either you're just burning a hole in your pocket

 

yeah..it is a bit dear on my pocket :P...ill try running standard fuel as well..i guess back in the day fuel wasnt as engineered as it is these days..thanks guys!