I have a 80s 351 in my 55 sunliner and need to put on a better set of heads,it has late 70s to mid 80s smog heads and would like to find a better set of factoory heads to put on it when I change the cam. I found a st of 69 or 70 heads in a junkyard but are there any late model heads that re just as good since the early heads do not have hardened seats. Jeff