X-heads vs J-heads: what's the difference??

im no head expert but from what justin used to tell me, unmodified X heads are the ****.
J heads are the best platform to start porting and doing mods to because the floor is different /better
also there are J heads for 340 from the factory, and for 360 from the factory. differnt intake valves ans valve springs.
you can modify 360's for 340 but it takes alot of porting and bowl work.