X Heads or J Heads???

X head =2.02/1.60 (in/ex)
J Head (early)=2.02/1.60
J Head (late)= 1.88/1.60 (Not 100% on exhaust pretty sure it is 1.60 though)
Both X and (early) J will work just fine and the (late) Js did come stock on 72 and 73 model 340s