Im not sure, but I was thinking. If I was around back in the day, couldn't I take one of them late 340's and slap a top end from another on and have an 'early 340' basically?
No, the whole rotaining Assy is different. Cast crank in the late 340's and low comp Pistrons V Forged Crank and high comp pistons in the early 340's. Im sure there is other differences too. :)