Short version-there isn't one and s bend stays look goofy w/a lugged frame- fillet braze it.


Long version-
If you were to put the s bend seatstays in a regular lugged shell, the dropout ends almost touch- meaning you'll have to bend the stays to make them work. Unless you have a bit of experience with bending the thin Zona-type stays, I wouldn't try it. Besides, the bending would tend to straighten the stays and that's moving in the wrong direction for tire clearance.

An MTB shell would have better cs angles but the st/dt would be way off for a road frame.

FYI, Columbus recently started making an s bend cs for use with lugged shells, afaik, R.Sachs is the only one carrying them.