So here are the drawings. You need to measure the thickness of the headstock side where the current tuners are placed and then choose the version based on that. You do not need a forstner bit, best bet is to get a tapered reamer and open up the holes assuming that the diameter of the UPTs is larger than the current tuners. If they are smaller you will need to plug the holes with a dowel and wood glue, and re-drill to suit. There are a few posts showing the process in a paddle headstock, they are useful as the step of using the reamer will be the same.
I don't know what year my tenor Risa stick was made. (S/N #15014433)
The tuners are not friction but look similar to UPT tuners. But are not UPTs. The base of the tuners are about 18mm, but there are no markings on them. They are mounted at an angle to the side of the Risa, tilted towards the saddle (heel). They fit into tight countersunk holes. The other end of the tuners also sit into 18mm dia countersunk holes on the inner side of the "body". The deepest side of the hole is about 7mm. The shallowest is about 4mm. (I marked a paperclip and measured the marking to the end.) The thickness of the wood is about 14mm. I have no way to measure the depths of the top tuner base side holes. The bottom peg ends are held in with a solid hex nut/washer unified piece that is screwed on over the peg end. Sorry, I don't have a protractor to measure the angle the tuners sit.
The thickness of the wood in the bottom of the holes must be about 7mm thick. Again, I made pretty crude measurements. Mine sit much higher in the holes than the ones in your photo. And look longer.
