I made head patterns for a 1914 Indian V twin and poured them in cast iron. The front and rear heads have a different exhaust port angle and take a 1 3/8" x 24 adaptor for the exhaust pipe. I used lost foam to cast fixture plates to hold the castings at the correct angle and then used a .375" thread cutter to cut the threads. The test plug was turned to the thread of an original head and sized out at 1.360" so I cut the new threads to 1.365 and it accepted the plug nicely.
This head had some cold shuts from a bobble, but it is nice soft cast iron. I started to bore with a boring head on the manual mill, but left it undersize so the center could be established on the CNC mill.
I transferred the head and fixture to the CNC and used a .3125" cutter to clean the bore using the thread wizard. Then I used the same wizard to thread the bore using three passes since it was a first time for me. Here it is with the test plug.
And here with the test plug in ready for the exhaust guide threads to be cut with a tap.