Yeah it's a Jews Harp also called jaw harp or mouth harp...found one and you can see where the centre piece was....unreal find...I've only seen a couple dug up this shape, and both were from very early sites...congrats :Y: ..people still play these things,can watch on you tube....twang on!
I used to have the 705 ..dug some very small pieces with it to...are you looking for relics? Great hobby to surprise yourself, and endless places to go!