About 10 years ago I replaced the original tuners on my F-212 with mini-Schallers. The original tuners on all 12s were Kluson six in line, changed to Japanese tuners around 1966. The original mounting holes had to be filled in for the Schallers to fit, and there still are the two holes where the top end was fastened. There was nothing wrong with the original set that some lubrication wouldn't have fixed, but I opted for the change. Because of the weight, however, I'd probably go with open-back Waverlys if I did it now. They would require some alteration however, as the body is too long to fit without trimming one end.
BTW, I still have the original tuners, and in the unlikely event I ever sell the F-212 (I've had it 45 years), I'd probably put them back on.
Brad