One big center inlet and two smaller outlets??? here is a block i did and am still remodeling:
Worked great with the half assed 1/2"ID looking center inlet and the two 1/4" outlets. Going to oval ot out a little more later when I get the time.
Have no idea about lath tooling although a vertical mills endmill should do the whole thing without needing sharpening if you are going to use a carbide endmill with coolant.