the problem I had is they kept posturing at eachother..and neither one knew the other one was posturing... they didn't understand eachother.. imo this is why sometimes it works and sometimes not.
and while FLG have teeth, they are used mainly in grasping prey.. my gar posture and occasionally will nip eachother but it is nowhere near as "active" as what cichlids and other truely aggressive/territorial fish do... Gar have a heirarchy that is establish with other gar... imo gar mistake arrows for other gar.. and this leads to confusion and aggression between two fish that don't undertand eachother sometimes. When attacked actively FLG will flee... which will lead to either being killed by an overly aggressive tank-mate( the gar can't get away and gets cornered and hammered on) or it will eventually hit the wall or top so hard it breaks it's back, or jumps out.
IDK how many or what species these other people keep.. But I atm own 2 FLG, 3LNG, and 1 CBG... The oldest is now 3yrs and I've had him the whole time.
Short term.. if your fish where juvies it might work.. but your talking some bruisers both size and aggression wise, and gar simply are not that aggressive until you start talking alligators, trops, and cubans ( which you wouldn't get from me since my cuban has only shown his dominance to my other gar but hasn't touched the rays or large spiney eel with him).
There is always a "chance" such combos will work.. but like I said.. I'de bet against this combo every time. It's not just one fish.. but as a group.