EP Swaps - someone smarter than me read this

can someone please explain to me why B series engines can take headswaps and D series engines can take headswaps but the D17 has to be a bastard and not swap with any other D series heads... i know it can't happen, but i would like to know why.

the d17 doesnt share the same parts with the older d series. im not sure about the d17s, but i think an ex head might work on an hx or dx block. ask Se7en, he might know more.

yeah, i know i can put the ex head on mine... but why would i want VTECe when i could just put a y8 head on there... too bad i can't put a Y8 head on there... guess i'll just find an A2 head.