Your handyman doesn't seem to have a clue about the valve and the trim for it.
You have to use the trim that is made for the valve in the wall. Either that, or change the valve in the wall.
What is standard, is the shower arm. That threads into a 1/2" female fitting in the wall, so any standard shower arm, or shower head will work.
The tub spout is also a standard 1/2" pipe thread.