Hey mate, use the GX dizzy with the A14 bottom plate, that way you have the correct advance curve for you GX Su's.

Exhaust manifold should fit no worries, head does interchange but you have to do something to get the oil to the top of the head, not sure exactly what, do a search, plenty of discussion on that.

EDIT: I think you actually have to fill the oil hole to use the early head on the later block, its the 74+ heads that have a different bolt to get oil up to the top of the head. Someone will know more.