Those heads were run both on 390 high altitude and with machined spring seats on 406 motors. I had a set that I ran on a .060 390 with tri power and it pinged pretty bad. The combustion chambers were 61cc. I had to go to a Comp 280h cam to get the pinging down to a reasonable level even though it still pinged if I had the initial timing at 16. I ran the timing at 12 to get away from the pinging which lost a little power. I had 427 long cast headers on it and it did run pretty decent.
