I didn’t weigh the original tuners to compare with the Gotohs, but my guess is that there is almost no difference. There is a Res-o-lite version of the GB707 and also there is also the new GBU line that is basically the Ultralites but even lighter.I’ve just installed these pickups and am quite pleased with the results. They work well with TI flats. While performing the swap, I did take the time to add some copper shielding to the pup and control cavity. I am strongly considering putting in the Trickfish preamp that is a drop-in for jazz basses.
Was there any weight savings? I’ve looked at putting Hipshot Ultralight tuners in, but wasn’t sure of the size. I take it that 3/8” is correct based on your experience installing the Gotohs?
I got the 9 mm version of the GB707 and they were a perfect fit. I think 3/8 will probably be fine or a little bit bigger than the original hole diameter. If you really want something close to Ultralites, take a look at the Gotoh GBU series.