320 Manual Safety

I'm in the process of converting my non-manual safety to a manual safety, so I've researched this. A notch has to be cut in the FCU for the manual safety lever and notches have to be cut on both sides of the grip module to accommodate the safety levers. Once those notches are cut, you can buy the parts and do the installation yourself (if you want). There are 4 parts you'll need: right and left safety lever, spring, and spring detent. You might need a new trigger bar as well, depending on whether you have the original style trigger bar.

AB Prototype offers the service of cutting the notches in the FCU and the grip modules. Check out their web site, they have pictures, etc. that cover everything you'll need to consider. If you're buying new, then I agree better (and cheaper) to just get manual safety p320. Also, SigSauerParts.com occasionally sells manual safety FCU's - my understanding is they take them out of new guns, but it is not something they stock consistently. If you're not in a hurry, you can just keep an eye out and wait until they have some. Good luck.