What is the proper process for tile over previously poured marble shower floor? ATTN PROS:
i.e. type of setting mortar, securing with metal lathe? ETC.

Let's first clarify what you mean by a poured marble floor, marble is a slab of solid stone. Do you mean marble tile or terrazzo?

Cultured Marble made from epoxy about 2 inches thick set on top of a shower pan liner.