FaL L1A1 is Australian I think
FaL Imbel is south american and much better than the autralian from what I hear, mostly because some Imbel recivers made it to the states and the L1A1s have century stamped on theirs.
but essentially these rifles are from the same design but I won't swear they will interchange parts. There are Inch pattern FALs and Metric pattern FALs also if you are really interested in a FAL and aren't looking for a Build or are later looking for a Reciver look up DSA. they bought the tooling from FN to build FALs, American made high quality guns from what I hear.
G3s and Cetmes are again similar designs but are different from FALs. they are a nasty, dirty, reliable, accurate gun. FALs use a Piston operated gas system while G3s and Cetmes use pure blowback, which dumps alot of burned powder back into the action. But from what I have seen with a buddy's Cetme it doesn't seem to really affect the reliablility of the gun any. and someone around here has said something about the G3 withstanding Cold weather better than the FAL.
but anyway FALs and G3/cetmes are not the same. Parts and Mags do not universaly interchange between them. the only thing they all have in common is the round they fire. I have looked at L1a1s and G3s and Cetmes and an Imbel FAL but I have only shot a Cetme. it had surprisingly light recoil but the muzzle break it had on made it want to jump up and smack you in the face. It also took some work to get working properly. Personally I would look around at them all read up what you can, and AVOID anything that says Century on it.