Factory WSMs come as short actions.
Longer bullets will normally require longer throating no matter long or short action. Otherwise they will be seated deeper in the case and limit powder regardless of the action length or the parent case. The reamer used by the smith dictates throat unless he is using a hand throater.
understand too that an extra long throat limits use of the shorter bullets without a lot of jump and not all like a lot of jump. That will be applicable to any chambering or long or short action .
Yes, the mag box will limit the COAL with either short or long action.
Work from there not what type action. That should be your starting point if you think you really have an issue with seating depth, versus vague generalities.
Lot of very good 168, 175 and 180s in 30 cal that will work in a WSM with Wyatts mag box and give you all the length you need. Wyatts box is $30. 180 at 2950 plus will handle anything in lower 48.
What bullet are you planning on shooting that is above the 180s and why do you need it? That question is applicable to either the Win Mag or WSM.
WSM case is rate for higher pressures than the Win mag and shorter more efficiant powder column allows the increased MV.
FYI the WSMs beat the RSAUM so that is going below the WSM. They do not split the difference with same bullet weights.
BH