This is still the big mystery but as far as I understand the Schaller M4s are the replacements but I have only seen them with the screws on the side. Except for the ones that come on the Euro series which are screws down. But this seems to be a OEM version used in the Czech shop.
If you decide to go with Gotoh's instead of the schallers I think you will need to route the holes bigger based on this diagram.
Thanks, Sam. I just emailed PJ to see if he could point me/us in the correct direction. It seems like the kind of thing that that should sell along with the bridges on the site. I'll report back on what I find out.
UPDATE: (I love that I can email a totally random question to PJ, and have a comprehensive answer in my inbox 12 minute later. Try that with /any/ other vendor, but I digress.)

Here's what he told me:
> Schaller tuners can be confusing. hopefully this info will help.
>
> M4 original version. this is what we used from the beginning mid 1970's thru early 1990's.
> set screw faces the center of the headstock, from the corner of the tuner.
>
> in 2000 Schaller decided to change this tuner design. and to keep it interesting, they continued to make both LOL.
>
> M4 2000
> same as above except set screw faces down toward the neck.
> also I have seen versions with slightly diff shaped tuning part (the part you turn, sorry it's Fri afternoon).
> we use these on our modern EuroLX basses.
>
> both use the same size headstock hole.
Hopefully we'll get some photos not too long afterwards...
(and no, it isn't me
)