most people wouldn't suggest smaller than a 75 gallon for oscars because of the depth from front to back. Oscars outgrow it quickly and find it difficult to turn around.
is a 36x18x20 55g going to be long enough for an oscar? your trading length for width
also,its not weird, its just not standard 55. I've been doing some shopping looking for an acrylic one. the extra width is really good for planted tanks.
The 55 breeder 36x18x20 is perfect for a single oscar. 18" is plenty room for them to turn. A standard 48" 55 isn't though. A friend used to have an 16-18" oscar in a 29. It was very sad and I kept telling her that he needed a bigger tank. That fish thought he was a dog and would just wait and beg. He managed to turn without any visible difficulty though when he did move around.
If you just got the Oscars and they are babies, the 55 could hold them for a little while but full grown, they would be the exact length of the 55 gallon width and turning around would be difficult. One full grown Oscar in a 55 gallon wouldn't work IMHO.