The column shift C4s had a different lever than the floor shift C4s. If you want to do the swap with factory parts, find a junkyard Fairmont or Fox Mustang with a C4 and a floor shift, and get the lever from the trans. This will require removing the pan and valve body to get to the nut that holds the lever on from the inside, install it and the shift linkage in your C4, and off you go.
If you don't want to do that, and have access to a MIG welder, you can make a new tab to extend the column shift lever to the floor shift position, weld to the lever, and hook up the floor shift linkage.
-Mike S.