Welcome to the forum !

Varmint barrel contour and you're right, it doesn't matter if it's center or stagger feed since it's a single shot.

Only the action screw spacing matters, which for the long action there is only one spacing.

From what I read in the past there were short actions with triple digit nomenclature (like model 112) with a screw spacing of 4.52"ish. But since you already measured your spacing to be 5.06", you know it's a long action and any long action stock will work.

Make sure you choose a long action stock with a Blind Magazine. But I'm sure you already know this.