Wicked bad blow back from bad rings can upchuck in this direction, but compression test should show that. Spark timing is computed by the ECU from CKP, Knock sensor, and others.. on the fly, per cyclinder. So you can have 8 different advances at the same time. But could still have slop timing chain. Unlike the D1 with stamped metal reluctor ring, D2 has a machined one that won't have a bent tab. You have gone this far, a couple of valve covers are not much of a challenge.

 

What would I look for buzz?