What a crazy piece of crap engineering on that one. I have seen a few Valley Valves made that way as well. When I was just a Pup, had an old-timer show me a trick to getting that cap nut off with out twisting the tubes. use a pipe wrench. set the jaw on the cap, then tap the handle with hammer or another wrench. The impact loosens the cap. Trying to muscle it off just twist the tubes.
at this point it pretty much doesn't matter what the brand of this on is. you can pretty much put anything back in. Moen Positemp is a good choice. I would stay clear of the Moentrol type valve( has a more parts to repair.)