I have a 70 Chevelle with a 355 automatic TH350 with a TCI breakaway Torque converter. Comp Cam part # 12-212-2. I'm not good with cam specs, but Gross valve lift .486. Duration at .006 tappet lift 280 degrees. Holley 670 dual feed street avenger. Acell distributor with stock HEI ignition. The old plugs were AC R45TS Gapped at .040. I have also seen short plugs for header clearance that I might need. Not sure of the manufactuer.

Appreciate your reply's.

Your AC's are the most reliable plug, NGK UR4's cross reference they work good also.

Dave