This is a great forum but sometimes you need to seek other resources to answer you questions. The problem with K98 collecting is that there were many legit variations produced during the war and perhaps even more variations created after the war.
Best Resources in no particular order:
www.k98kforum.com
Law's Backbone of the Wehrmacht
Kriegsmodell book
g43forum.com
http://www.ycgg.org/ycgg_ww2german_pdf.htm
From the research I have done a cupped buttplate stock would be correct. The stock should have a Waffen amt "63" or "655". You are fortunate because most surplus stocks that one can find are cupped buttplate stocks and usually have one of these two Waffen amts. Mauser Obendorf was a large producer of stocks and even subcontracted to other K98 producers, they also made replacement stocks for Waffen Meisters.
1941 is an intersting year, because in 1940 and 1941 several changes took place. Please look at the reference below by Robert Jensen:
"The waffenamts on the code “42” rifle changed in 1940 from Waffenamt “63” to Waffenamt “655”.
Some “no” letter range rifles can be found with the “63” proofs. A Mixture of “63” and “655” proofs can be
found on the same rifle in the”a” range but as soon as the “63” proofed parts were used only the “655”
proofed rifles appear. Flat buttplates were discontinued late in 1940 and cupped buttplates were used to
prevent the separation of the Butt stock. The known serial number for the code “42” 1940 rifle is from 1660
to 5499gg with an estimated production run of 340,000 rifles. Subcontracted parts, such as the buttplates coded” bpr” and “brg”
appear. Kriegsmarine, and Luftwaffe rifles are known to have been produced in 1940 but no examples have yet been reported.
In 1941 the Mauser Oberndorf manufacturing code was changed from “42” to “byf” and the
receiver date was changed from a four-digit to a two-digit date. Army and Luftwaffe rifles were produced
in 1941. The front sight hood was introduced. Small parts (bolt parts, floorplates, followers, and front
sight bases) with Waffenamt “WaA103” and “WaA140” proofs were used (made by F.N. in occupied
Belgium). The known serial number range for the 1941 “byf” K98k is from 4514 to 6474hh with an
estimated production run of 350,000 rifles. Luftwaffe issued s/n 1059I has the luft acceptance proof
stamped on the right side of the butt stock."
I hope this helps.