What you have is a K98b not a Gew98. A very very rare rifle especially in matching condition, but sadly someone turned yours into a deer rifle after the war. It is hard to look at! Like M99, I doubt very much the mounts are period.
Can you take a shot of the other side of the receiver where the proofs are?
If it was a Kar98b it would be marked as such on the receiver.
Do we havr any clue how many of these were made?
I have uploaded your right receiver pics here for posterity. I hope you do not mind.
There are several side rail variations with the 98b. Gew98 was one of the them.
My own feeling is you are technically correct, as the Karabiner 98b nomenclature had not been "adopted" (I use that word loosely) when this rifle was manufactured (happened later in 1925). Still, any rifle made by Simson and dated we call a 98b. This rifle is very rare, and worth restoring properly.
By the way, what is the serial number on the front scope ring, on the side? Looks like a High Turret scope and rings!
Scope serial is 50265, serial in the forward scope ring is 40274. Any idea on the vintage of the scope? Would like to figure out when the rifle might have been modified, I would assume this took place while it was still in Germany. I have owned it for 36 years and was told it was a WWII battlefield acquisition by the Grandfather of the friend I bought it from.