[vettestr]

A little more info would help all be able to give better advise. Do you know any of the engine spec's? What is the compression ratio or even what is the cranking pressure from a compression test? Do you have iron or aluminum heads and how big is the camshaft, does it lope hard or idle pretty smooth? What is the initial and total timing set at?

Some of the questions above will help get us closer to a educated guess and you may be able to even run a lower octane rating than the 100 RMS mentioned. If you are not an engine guy the cost of taking it to a shop to help answer or determine the needs of the engine would be repaid quickly in saved fuel costs or saved engine parts.