What your gonna have to do is clean than dual case assembly. So, you can look for some stampings and markings. Above the front output shaft you will see some markings like these in the picture.
But from what I can see in your fuzzy picture, the stampings don't match the ones in picture from Marlin. So, you will need to get dirty. And if you can find some engraved numbers. All adapters and transmissions (IIRC) have numbers and Marlin keeps records on what number was sold to the original purchaser, and whether it was just an adapter or a full setup and what gears were installed. Stock 2.28 or 4.7 gears. So, get cleaning and let us know what you find out.
