There is only one action length. They do change the length of the bolt travel for different cartridges by changing the position of the bolt stop. The magazines for the shorter cartridges have spacers in them to correctly position the cartridge but from the outside they are all the same too.
Sako uses different length receivers for the various cartridge sizes. To me, it's not a significant drawback (what's a couple of ounces of weight....the T3 is incredibly light already). I have a T3 and love it, though I am selling it soon to make room for (gasp) a Savage 99 in .250 Savage. The gun cabinet is full......maybe I should instead get a new gun cabinet.....?