Perry,
the 7.62c39 is still a very good cartridge in itself!
My 2 cents leave as it is..........However to convert to 7.62x54R would be certainly a big step up!

I wonder if you can get replacement barrels for your rig???
You would just change barrels if you want a new calibre for different game.
.223 etc for small game/pest destruction
7.62x39 for short range work on medium game
7.62x54 for the heavy stuff
But one in 9.3x74 would be a hoot - casting would certainly be an option then!
Only issue - can you get extra barrels for these rifle?
Cheers
93x64mm