You're on the good way. The use of a vice is a smart solution. I could imagine they original owners after 1945 had stopped using the ominous Germanenmesser-inscription for export. Or, even more likely, it is from before the introduction of it, end twenties, as a political statement. The narrow fingerguard and absence of an integrated virole is similar to German vintages of that time, and the modern Herder 1922. Other than modern ones, even replicas, this one looks to have been produced by hammer forging. Hard to believe the new owners of the name after the bankruptcy started in the seventies by producing what was already in those days an extremely labour-intensive niche-product. They rather made cheap stainless butchers' knives, as far as I've seen.
As they're is no active rust the pitting seems stable. I wouldn't touch it.
I would indeed aim for a fingerguard that's 0.5mm / 3/16" lower than the final edge, and not insist on thinning the last millimetres close to the fingerguard. It is likely to cause an overgrind just before it, as I've experienced. Knock off the shoulders, and have the bevels flush with the faces. The whole idea is having a robust first part at the heel, and a thin front with a spectacular distal taper, having all functions and uses combined in one knife.
