Thermoquad on 340 (plug photos)

Might have an intake manifold leak. That will cause a lean condition too. Those tq's were notorius for being on the rich side to begin with. Just another thought. Seen that before on a 440 w 850 dbl pumper. Crappy metal gasket. Car seemed to run normal but always lean. Bought another carb thinking it was junk only to find that out later.