The Tikkas (T3) all use the same length action. They just have different bolt stops and magazine blocks.
Edit- I should add that the magazine blocks can be removed or modified and the bolt stops switched from a SA to a LA which will allow seating the bullets longer on some cartridges. (Providing your throat is long enough in your rifle)
The magazine blocks are part of the magazine body. They are a PITA to remove! You need to take the floor plate, follower, and spring out, then cut the back spacer out with a Dremel and small file. Then glue in a skinnier aluminum chunk of miniature C Channel. I did a couple conversions from .308 to 6.5x55 on magazines that I got at a yard sale. Now I just buy 10 round mags from Australia.