The only phone number I could get at fed mogul couldn't answer my question.. I have been using the 1009 head gasket on most BB builds ,,now I go to most any auto store and all they show is the 8519 gasket .. they look the same, but is the crush dia the same ? is the bore size different ??..I could order the 1009's but they are $ 53 bucks where the 8519's are 18 dollars ..I can't see the difference in the gaskets when held next to each other ,,,Anyone got the answer ?? Or a # to call?

https://board.moparts.org/ubbthreads/showflat.php?Number=6134460


Thickness was mentioned there..

i use the 8519's and to my knowledge compressed thickness is the same. 8519's don't have the "wire" in the fire ring and have a larger bore. personally i think they're more reliable in the larger 400 and 440 bore. just my .