12:44:38 - That would have rattled hard!
12.6 - 13.7 on 19-20 psi would have been it's death knell.
That cat of yours must have been severely blocked if clearing it shifted your AFR's 3 points leaner than it should have been.
FYI: I run similar heads to yours (same combustion chamber design) - my safe AFR at 22-23 psi is 11.2:1 on Bp98 with 15-16 degrees of timing.
Invest in a wideband O2 dude - Techedge 2J or similar, it will save you $1000's in the future.
Time to build something stronger now!
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