Based on the coloration in those pictures it does look like an amazon sword. Once some submerged growth appears that can help confirm or deny. I think you'll be ok putting the sword in your 55 if it is an amazon. Those really don't require much light.
Here it is.
I also found a snail. Which is weird since I have never seen one in the 3 weeks I've had this plant. I'm kind of glad though since I was thinking of going to the store to get some so I can put them in my 55g to dig through the sand. Hopefully I find some more!!