Red Armoured Train Machine Gun Wagon

I finished the twin turret machine gun wagon for the Bolshevik armoured train today, so can now move on to the locomotive and tender. The Contemptible Little Armies rules allow a machine gun wagon with up to four machine guns, two firing to either side, but have no reference to turrets other than to cost them at 150 points each. Anyway, whatever the cost, I'm thinking of adding another machine gun armed wagon to the train but this time with only one centrally mounted machine gun or one fixed gun on each side to keep the cost to a minimum.