these are both oem.  never touched. if you look on the tops of the heads you can see one is E1 the other style is E2 the one with the smaller dome (E2) is off of a 87 if i can remember correctly and the other(E1) is 88-92.  i have several sets of both styles and always wondered what the cc difference was but could never find any specs. ill have to research on how to measure them myself. i thought there might be someone on here that would know off hand the differences. thanks for the the feedback