J (915) vs. Magnum heads

2 different beasts if you really want to get into it.
magnums are modern, and in stock form will probably do better than J's
Js have way better longevity, and porting possiblity. you know the Js need a valve job, so hardened seats mill you will have alot into Js.
But if you are building a motor the Js nice.

rusty you are correct he hates magnums. lol i would never want to run them myself either, unless maybe they came with another fresh set to swap in when they crack. lol