Might be to exchange that old and likely expired tank for a new one. Perhaps I'm missing something though.
A lot of the propane dealers that have a customer service will swap those valves for you. That said, it will probably cost more than if you just swap the tank at an exchange station...unless that's one of the larger sizes. Besides, like Blackhat said, that tank may be out of date and need re testing. Call a few places and ask if they'll install an OPD valve for you.
I thought about swapping it out but I got it free and it has a full 20# charge of propane.
I uderstand your thinking but spending $20 to use $8 of free propane isn't a deal. I have appliances and 100lb bottles that still use the old style connectors so I own the fittings to swap back and forth. If you are going to use it a lot, a weed torch or similar that still has that connector style, or better yet, a dual style connector may be the best route.
That appears to be an old style propane tank. Propane dealers cannot legally fill those tanks. As someone mentioned, the valves can be replaced but the best thing would be to exchange it or buy a new tank.
There is a fitting adapter. I bet it costs $20.
The tank is out of date. The best way I have found to use up the propane, is to lend/give the tank to someone with an RV. All the RVs I know of use the internal thread connection. Then you can toss the tank, and save your money to purchase a new in-date tank.
My weed burner used that connection too. Ship me that tank and I'll mail$20.