The problem with the CSV1W was that when the government made us switch to Low lead brass, the insides flake off in little green chips of copper. This can make them hard to disassemble. But if you can get the gut pack out of the CSV1W, you can remove the seat with the rubber disc and put the rest back in the valve, then it will work like a piece of pipe. But you have to put the diaphragm and top part of the gut pack back in to keep it from leaking from the adjustment screw.
If you get this done or remove the CSV1W completely, then you can add another CSV anywhere upstream of that location.