Back in the day we used this...
I'm ambivalent about brand as long as a bump safety has to be fitted. I've used WC and Brown, maybe others. That combined with setting the tine on the sear spring should do the job. @Robinson's warning should be heeded. The line between perfect and junk is pretty thin. When I fit a grip or thumb safety I spend way more time assembling/disassembling than filing/stoning.