for the gt40 y and x heads you must use #agsf-32c not sure what # this is in autolite or another manufacturer. stock plugs for a 5.0 are not the same, the number of threads and how far the electrode extend into the head is different. by experience i know because i ran stock plugs for a while not knowing, plugs fouled up very easily and car noticably ran hotter. make sure you get the correct plugs
go to fordracing.com or open up your ford motorsport catalog and it says must use agsf-32c, i dont know what the difference is with the ones your listing just make sure they are the same, you will notice a drop off in power and how your engine runs, double check that those #'s cross reference, if "awsf" is the same as "agsf" your good, the difference with the "32c" and "42c" is the heat range. the "32c" is one range colder
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