Left side of the motor there should be a coin with the model and serial number of the engine indicated, on the left drop out for the rear wheel there should be a serial number of the frame.
Could be a AV37 they looked like that in '54 and '55 or later AV3x, 4x, 5x because they adopted the look of the AV37... would need to look see the left side of the bike as well if it has a simple clutch, dimoby clutch, 3 speed auto or variator to determine which 'x' and prefix. Motobecane stopped the tube frame after the 1960 model year so it is 1950s. Looks to have a collection of not Motobecane parts on it so hard to peg it down better.