AC R43 plugs are pretty cold. I'd switch to R45 plugs like JW51 suggested.

Note the comment from Bartamos above "From Champion Spark Plug Co. Soft, black, sooty dry deposits on plug indicate carbon fouling. Carbon fouling is an indication of a rich air-fuel mixture, weak ignition, or improper heat range (too cold)."

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.