Mas 36 date ?

Cookie91/38:

If your rifle is not a Mle 1936-51 of the mid-"G" series, then that is the date its replacement barrel was first proofed. I am assuming that by the "underbelly", you are referring to the barrel's spanner-flat? Normally the barrel supplier's code precedes the date, but as I am not familiar with this late code, I am at a loss.

Cookie91/30:

It looks like your rifle received a new barrel about ten years after it was made. No visual difference would exist between a 1949 barrel, (which may well have been its original barrel date), and this new one. Both are post-1948, post-painted finish, and they would have the 5mm factory rebated muzzle which is "G" marked to indicate that they were suitable for use in grenade launching.