Since I could not find a 1/2" sweat valve, I had to use a 1/2" NPT valve. In order to mate with the rest of the engine, I had to use a couple of 3/8" adapters. Since I didn't want to see the adapters, I soldered them in and machined off the excess. Unfortunately, the threading did not extend deep enough into the valve, so I had to re-thread them. Threading brass was not as easy as I thought it would be, Today I only managed to do one of the the two. The other one will have to wait until tomorrow.