First off, I seriuosly doubt the seats are any different OD wise for any of the minor differnces in valve diameter being discussed. And, B, odds are you don't even need or want said seats. Why would you think it wise to hog big a$$ holes in your vintage heads and pound in steel rings? Classic case of the cure being worse than the disease. For what it's worth, I'm currently running 2.14/1.88,s in a well hogged out set of 915,s and short of having to do minor bore notching for the stupid big exhausts that some prior owner installed, everything is just fine. Of course this won't work for every set of 40+ year old set of heads but why worry? If it becomes that troublesome, sell 'em and buy new....Just my opinion