120 gal is not to small for a porc, providing its a small one. Most times when you buy them at LFS they are only 2" big. They dont grow up that fast.
Also to if its a small porkie, then I have seen time and time again wounds that the eel did. You see it all the time, a porc got his tail nipped. I dont recommend Porkies with Eel, but thats IMO.