Correct, the really early models, 60's, did not have a bolt hold open on the receiver. Later they changed the charging handle to have a pin like piece cut out and a hole drilled into the receiver. Later they started with the LSHO. The bolt was cut a little different for the later models, 70/80's to accept the charging handle with the bolt hold open. The point is, the receiver and barrel should fit any stock but the trigger guard will be different depending on the age of the stock but will still fit the receive and work. If I am not mistaking, you would have to get a newer bolt and charging handle with the nipple on it and drill a hole for the nipple to fit in to get it to stay open. I have two oldies that I don't care that the bolt doesn't stay open, old school... I like it.