I've never heard of a M57, but that doesnt mean it doesnt exist.
One picture doesnt tell the story, but, from what I do see, it could be a M-37 with lots of local fabrication work.
You'll need full all around pictures for people to see to sell it, so they can figure out what it would take to strip that junk metal off of there and rebuild.
Then too, its kinda neat and unique as it is, and a buyer may just want it just like that.
Good luck.put up some more pics and list it in the classifieds. m-37s are bringing good money today.