Need advice on adding a florida gar

I have a 4' 120g (4x2x2) with 2 endlicheri (about 12"), 1 wild oscar (about 9") and a male con. BB with driftwood. I have the opportunity to pick up a 12" florida gar. My worry is that my O is an SOB. He is a nasty guy for his size. Think I could successfully add the gar? Any suggestions on what or how to do it so everyone comes out relatively unscathed?
Filtration is ac110, c360, emperor 400. Temp 79. wc's 30% 3x a week.

hmmm...maybe i should kick the O to a 75g I have empty and then it would just be the polys and the gar. Would that work? I don't want to get something irresponsibly, but gotta say, LOVE the gars and want to see if I can make my setups work.

Yes, its a convict. I would move it with the O or I have another home lined up for it. Thanks for all the input.

Its a tough decision! I wanted one from the get go and the opportunity has arisen, however I don't know that I have done enough research. Do you have any outstanding links (I read the stickies) on gar care that you could share with me?