The plugs that have been used in my car were NGK BR6ES and Autolite 404. At the recommendation of a parts store I purchased Champion RN14YC. I noticed that the thread reach is the same but the overall length from the thread base to the electrode arm is about 1/4 inch longer than either of the other plugs I used. I purchased my car pretty much done and don't know if the pistons are dome or not (previous owner couldn't remember). The heads are L34 and the bottom end is 454. Can anyone tell me if it is okay to use these plugs whether or not I have dome pistons. Some people I've spoken to say it doesn't matter, dome or not there is still plenty of clearance. Thank in advance for your replys.