67 383 spark plugs/what ta use?

I would say if it is a 1967 factory 383 car then it came with 516 heads that had the smaller intake and exhaust valves. Moving to the 915 closed chambered heads on the 67 hi-po 440 cars would be a good step up. Even better would be to put oversized intake and exhaust valves I think approx 2.18 and 1.81 not sure about exact size. I think factory was 2.08 intake and 1.74 exhaust. Also a big carb and better intake in combination will really wake the motor up. Any body else care to chime in.