absolutely, remove the plate with the 2 screws and then you can access the gearbox.
you HAVE to remove the barrel (either receiver-barrel or just the barrel) before taking out the gearbox or you'll risk to break the cylinder head's nozzle while doing so.
The gearbox is not held in position by screws or anything so you just need to shake it out of the body; beware of the shell ejector shutter, it's mounted on top of the gearbox and comes out with it.
you are removing ST21, and taking out blocks ST25, ST26,... to 31.
