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A short FAL carbine, featuring the classic folding stock, as well as a desert camo painted on with Cerakote. The extended 30rd magazine is from a British L4A1 light machinegun, which is a conversion of the classic WW2 era Bren, from .303 British to 7.62mm NATO, this conversion would use FAL pattern magazines, for commonality with the then new rifle of the British Armed forces, the L1A1 Self-Loading Rifle.
This was probably more to let the L4 use rifle magazines, than it was for the rifles to use the L4 magazines, with the L4 being a Bren and having its magazine on top, gravity normally assists in feeding, which you don't get when inserting said magazine into the corresponding rifle.
It would kind of work, but misfeeds would not be uncommon, the trick in the field would be to disassemble the magazine and then stretch out the magazine spring some, but I imagine this affected the spring's lifespan, since you were not allowed to do it. Australian spec-ops in Vietnam had been seen using L4 magazines in their rifles, likely they would replace the spring or otherwise alter the magazine to make it more permanently suitable.