Antonio Labriola – any good?

Yes, it is. He’s quite good on the materialist conception of history. But don’t mix him up with the syndicalist/reformist Arturo Labriola. Translations of his writings, published by Charles H. Kerr in Chicago, are in the Party library if you want to borrow them.

I’m not quite sure what you mean by “original”. He was the first titled professor of philosophy to embrace Marxism (relatively late in his life) and was highly regarded in the pre-WWI Social Democratic movement because of this (that’s why more than one copy of his books are in the Party library). His interpretation of the materialist conception of history was less economic determinist and more philosophical than some other interpretations. You don’t necessarily have to agree with him but he has a prominent place in the history of “Marxism” and ought to be read by anyone who wants to know about this along with Kautsky, Plekhanov and the others. You can dip into his writings on the Marxists Internet Archive here.