I don't know if this is the rough opening or finished in opening, but regardless its oversize.
This will work if you want to shrink that opening to accomodate a standard door. that would not be difficult at all.
open up the opening to a rough opening, and then get your door kit with frame. then create a new frame on the opening that is about two inches wider than the door kit and about one inch taller than the door kit.
The key is a door KIT with frame attached. Build up the hole with 2x6's and one inch drywall.