I have not had more than one spilo so I can not speak from experience, however, From what I have read I dont think they will last that long in a 55. if you grew them to 4-5 inches you may be fine but they are tougher to keep together than pygos and I believe they need more room to shaol successfully than a shoal of pygos.
That being said, if you get them together early like 2-3 inches it may work. I would try it, I love my little spilo so worst case you end up with one in a 55 which isnt all bad. I think you would have better success if you tried 3 in a 75. But like I said, I have never done it so what the do I know