The problem that I see here is we're talking about this stocking in a 75 gallon tank. Personally I think an oscar and a pleco is all that size tank can handle, unless it is severely over filtered. Even then, a full-grown oscar will dwarf a 75 gallon tank.
You have to keep in mind that oscars have enormous appetites, and mouths to match. If it can fit in the oscar's mouth, the oscar will eat it. If it is smaller than the oscar, the oscar will try to eat it. A good rule of thumb to follow with oscars is this: If it is half the oscar's size or smaller, it's probably too small to keep with an oscar. Spiny eels are nice looking, but I rarely see any that are large enough to not be oscar food, and when I do see them, they're expensive. My lfs sells peacock eels for about $5, but they're about 3 inches long. A 4 inch oscar would have not problem eating several of those.
"Share what you know....or shut up and learn what you don't." - OinKY