It would be an AKM with a drum mag. The RPK has a reinforced receiver that is aesthetically different. The barrel would also be too short for you to mount an RPK bipod. If you run it with regular magazines, then you're just using an AK with a bipod, there's no need for special rules.
Not for glory, nor riches, nor honours, but for freedom alone, which no good man gives up except with his life.