Litschert produced the boosters for a lot of different scopes (starting in the 1940s, according to Nick Stroebels book.)
Yes. I believe it should make it either 6x or 8x power when installed.
The scope on the left is suitable. (It's likely a post-war scope but close enough for a WWII replica). I recall that to use the old Litchert magnification boosters, one has to remove the original objective lens - or that was at least the case with the Weaver scope that I had with an 8x Litchert booster. So, unless the German scope on the right still has the original 4x objective lens, or one can be found, it is not really suitable for any type of "replica" K98 sniper. It's a neat looking scope and they were used by civilians back in the day. I recall in a book by Peter Senich or Brophy(?) that the US military did perhaps evaluate a prototype Litchert magnification booster at some point (WWII or maybe Korean War?), but never adopted them.
Mr. Litchert sold magnification boosters for various scopes in the 1950s and maybe 1960s. I once bought WWI Mauser that been sporterized back in the 1950s/60s as a heavy barrel varmint rifle in 22-250. It had an old 2.5x Weaver scope with the 8x magnification Litchert booster threaded into the end. It was called the "VARMINT MASTER". So basically you could turn a Weaver 330/440 series 2.5x or 4x scope into an 8x, 10x, etc, based on how large/long the new booster was. It required removing the original objective lens from the scope, as the focal length was much longer/stronger with the booster. I sold that scope several years ago, but kept some pics:
