"...Hmm external piping-be interesting install, not sure Im picturing as faucets are thru the wall or sink/counter. But yes the valve is direct to the shower head. ..."
I'm considering some kind of hollow spacer behind the valve to make room for water line hook up.
Thinking the valve itself could be located higher than normal to get it out of the way , maybe upside down in the corner with shower hose coming out of the bottom instead of the top.
Can the threaded ends on the faucets where the water lines attach be cut shorter?
That would gain a tad bit of room.
I too dislike the twist off shower heads so I have kept the factory plastic one on the end of the hose because it has a push on/push off valve built in.