Another 87 octane/aluminum heads question

Keep in mind that thermal transfer is directly effected by the surface-to-surface pressure. So most of the heat is going to transfer where the pressure is greatest: around the outer edge of the ring, where the interference fit is located.

Now, the shop's skill is an entirely different matter LOL. And yes, a seat falling out is normally followed a short later with the symptoms you describe....

If you are really are going down this road with the higher CR and going to below sea level, then certainly aluminum heads can help. But you are counter-acting all that help with the higher CR. And unless you change to .028" head gaskets, then your quench gap with a closed head is not going to be worth much at over .050". So you are in a tight 'performance corner' here and need to look elsewhere for relief.

IMHO, for this and the fuel, you need to look more into the cam, and go with one with:
- A wider LSA like 114 which will help lower the DCR and reduce overlap for better economy
- Keep the intake opening later and the exhaust closing earlier to help reduce overlap for economy.
- Make it an old style sloooow ramp cam. 60+ degrees difference between advertised and .050" lift durations is where you need to be to drop that DCR.
- That was not uncommon to find in the mid-70's when guys were putting in smaller cams after the Arab Oil Embargo in high compression engines. Crane had a series of 'HE' (hydraulic economy) cams for this problem; I have a cam card for one with over 60 degrees between .050" and advertised lift: .050 durations of 190/200, and advertised of 254/264, on a 114 LSA (This was for a 351C). I see that Racer Brown has some profiles that are in the mid 50's degrees of difference, and Erson has some RV cams with a spread over 70 degrees, so maybe give them calls and explain the situation, once you settle on the heads and can get some real SCR numbers computed.

Edit to add: Dang, I read you current cam specs one more time.... missed all that! Looks just like I was telling you to do above LOL.

May I ask under what conditions the AFR is running in the 13's? If this is at 2500 RPM and cruise conditions, that is too rich for decent economy, carb'd or TBI. Folks get hung up on staying with stochiometric AFR all over the operating range, but that is only needed at more open throttle conditions. For moderate cruise at 60 mph on level ground, your AFR should be in the 15's; no problemo with the engine running OK. Heck, Chrysler Lean-Burn engines ran up in the 18-19 AFR range!