Personally, I wouldn't do a pair in a 55 gallon. I felt my 1 JD (although not an EB) was crowded in there. You might have luck, but I would have well established territories, maybe a large piece of wood in the middle or something and some sort of hiding place on each side. That is just my opinion, YMMV. You will also have to do very frequent PWCs and have very good filtration. I was doing a couple PWCs a week at 20% with 1 JD.
A mated pair of convicts might be your best bet in a 55, if you want a pair.