Welcome to the forum, Zanba01!
I agree with almost all that has been said above. You are getting good advices.
The following are just my opinions.
Yes, it is an RTCxTSN hybrid. Yes, it is probably stunted. How bad, no one really knows - e.g., if you put it in a lake, it could still reach its potential of 4' in 3-5 years, may be even 5' or the stunting could cause it to stay at, say, 3' max. In any case, you should think of the semi-worse case wherein it will reach 4' if you give it proper care. So, your step one is not to think of tankmates but rather to think through if you can provide for this great and beautiful, majestic pet.
If you think you can, then let's think about tankmates. If not, it's a moot point. So let us know if you decide to not find it a new home and keep it for yourself and then we will mull over the potential tankmates...
... my prediction is it will eat your gar(s), sooner or later - in a small tank (yes, 8'x3' id still small for this cat when sub-adult/adult) such a big predator will have no problems whatsoever catching any fish that will fit in his mouth girthwise - cigar-shaped gar is perfect for it. My hybrid just like yours only at 2.5' ate a 2' longnose gar in a 4000 gal pond (40'x6'x3').