7 stw action / ultra mag action

Hey all,
A friend of mine has a 7 stw that he was thinking of making into a 338 edge. My question is... were stw's built on ultra mag actions? I am about 40miles away from him so I can't check myself. The only difference is the magazine cut-out, correct? Worst case scenario- it's a single shot then, correct (without milling out the bottom of the receiver that is)?

anyone? ttt

STWs are Pre ultra mag. So no, the STW was not built on an ultra mag action. The port may be the same size, as the early actions were also used on H&H rounds