Retorqued intake manifold using 12mm 6pt flex socket, 3" extension, and inch-pound torque wrench; three equal rounds: 68, 136, and 204 in-lbs; final = 17 ft-lbs. per factory spec for the intake.
(note: had to pull fuel rail and move clutch cable, throttle cable, PCV valve & hose for access.)

Warmed up, check and adjusted ignition timing.
(maybe, one more timing check to do with "kill ECU adjustment" jumper in place; blue unconnected 2-wire plug near passenger door hinge.)

Basically, it looks like the problem is solved.
Now, I have to tweak the throttle cable slack a little bit (it's actually idling a little high now; factory spec is 10-12mm deflection; a simple one wrench fix).