What Mosin conversion are you talking about?
Finnish standard was the 7.62x54R cartridge. Non-54R weapons (such as the 7.35 M38s given to Finland by Italy in 1940), if they were even issued, were generally relegated to Civil Guard or other rear echelon units. The same would have been true for any 8mm rifles. Finland did have several thousand K98a purchased from France in 1919, but virtually all of them were sold to Poland in the '20s and '30s. They also apparently purchased 600 K98k along with German grenade launchers for testing in 1943, but that was it. I don't think Finland was terribly interested in any non-54R rifles or machine guns, so I don't think K98k were ever used by the Finnish Army outside of some limited testing. I am not aware of any SA marked examples either.
There is a three volume work on Finnish military small arms "Military Small Arms in Finland 1918-1988" by Markku Palokangus that discusses all of this in detail if you are interested.