Kwattro,
Sorry, should have been more clear that the other parts fit too.
For the upper butt plate screw I just found a nut that fit the screw and it fit in the slot in the stock. Can't give you an exact size as I dug it out of the spare hardware drawer on my bench.
Someone had posted earlier that there were some bolts (stove type IIRC) that were a dead ringer for the rivit heads on the USGI stocks.