The consensus is that the simplified bipods were among the last to be produced during the War, out of whatever was still available.
They are described in Folke's first book on page130.
"Later, the MG42 bipod was redesigned and simplified...."
He mentions that the studs that hold the bipod open were "troublesome".
Of course, when the Yugoslavs re-tooled for their production of the M-53, they copied the German "adjustable" MG42 bipod.
My MG42 receiver is marked "PJ" much like the bipod leg.
The part number doesn't look like the typical Yugoslav "S-....." we see on their parts.
I think you have a rare one. Congrats...Phil