GT40 Heads and Spark Plugs...PLEASE HELP

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I have gt40 heads on a stock bottom end the heads have new valve train and the valves were lengthened(I believe I cannot get ahold of the guy that did the set up so now Im stuck)...I decided to change the plugs today and found #5 Black and Gunky. I pulled the plug: AC Delco 41-985 When I went to Kragen they only could cross reference this to an champion double platinum. It seems these plugs fir a Z06 Vette and other misc. chevy trucks.

So I am not sure what to do...dont know if there will be any clearance issues or what gap should be...I believe the gap is set at 50.

Any help greatly appreciated since the car is apart.

Thanks in Advance

 

[SVT32VDOHC]

My GT40 aluminum heads had longer threads for the plugs. Murrays had the correct length and heat range Motorcrafts, but at that time I used NGK TR6's because they were the hot ticket in 2002.

 

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Plugs

I was able to match the plugs via cross number.

Should I just use these plugs tht I found or try something alse. The guy who did the motor said he lengthened the valves or something...will there be any issues?