The stock is from a FN, but is for a model 1924 which had a intermediate length receiver. FN also made the model 1930 which is a standard length receiver, your rifle should drop right into one of those and would be "correct" as a Yugo rework. I think FN made both a model 1924 and a model 1930 that used the waffle buttplate.
That's definitely not the stock that the Yugoslavs put it into. It should have a cut-down Gewehr 98 stock, and should have the bolt take down ferrules and Imperial proofs, among other aspects.