The best way to follow the FN M/98 from a "full military" configuration to a "real sporter" action is to have a close look at the HVA (Husqvarna) 640 series.
From 1946 to somewhere in 1947, they used, as you said, the military action, standard "C-type" with thumb notch and charger clip lips on the rear bridge.
1947 saw an intermediate form of the "sporter" action; they removed the charger clip bridge lips (but they kept the "hump") and made the action "solid wall". This action was still a "C-type".
Then, in 1948, the "H-type" appeared; it shows the hump, ont he rear brige and the "solid wall" with still a wing type safety.
All the above had the standard floorplate, not the "improved" ones.
Late 1948 to early 1949, the 'hump" of the rear bridge was removed, and in the same period the rear bridge was d&t for a receiver sight and the new floortplate with the modified catch (and hinge) and a low scope safety was used. Just after that came the D&T for the standard Weaver type bases.
You can find some of these variations on different posts in the Civilian Swedish forum. I am by now working on a database with pictures of the different types used by HVA.