I have done a little looking into this, and from what I can tell is that (now don't quote me as I could be wrong) that the serial numbers like we have are the newer machines. Probably made in the late 60's or early 70's. My side cover you remove to change stroke length has a newer South Bend logo on it compared to the others I have seen. Also on that same side cover mine has never had a tag on it describing the oil pump and its operation. I came to this conclusion by looking at all the old South Bend catalogs I could find online. So as far as I can tell they are newer. But like I said before, I could be wrong.
