my 400HO is all stock, except for 10:1 pistons. 100 octane?!! There's no way I can get that here- we have 91 at the pump, and no other sources that I'm aware of. However, I've had the 10:1 setup for over 20 years, and have had no problems, even with today's 91. There is no audible pinging, even if I stomp on it. Also, I've never had any problem with my valves, despite having stock valve guides and running unleaded for 20 years.
