I got my 1349 in the first year of release, whenever that was years ago.
The flat plate has a simple brass bolt passing through from below to engage the head on top. It's not reversible.
However, the stud in the column is reversible with the 3/8" thread along most of its length and a smaller 1/4 inch portion at one end. Mine is very loose, requiring the nut to pull everything tight. The column itself is threaded for 3/8" and that's what engages even when the short 1/4 inch portion is upright. Interestingly the column is threaded 3/8 at each end, with the bottom covered by a screw-on cover.
Could be the specs have changed over the years, even if the literature hasn't. The stud in my column is so loose, I can't imagine why yours is so tight. Sounds like a call to Gitzo is in order.