Do the math you spent over $2500.00 over 87 octane during that 50,000 miles. Cheaper and the correct way for the OP to have the harden seats added now.
The Road Runner 383 had around 10:1 compression ratio, and iron heads. You had to run at least 93 octane in it. I think the Amoco Super-Premium was even higher than that. Perhaps you missed the point of my post: I ran unleaded gas in a high performance engine without hardened valve seats for over 50K miles with no apparent damage.
