I bought an "apron" on E-bay to get the half-nuts. The picture looked just like my old 9" South Bend's apron. When it arrived in shipping at my workplace, I was delighted. It was clean, and the half nuts were near perfect. I envisioned just bolting it on the old SB at home and be running in 10 minutes. When I got home, I found that the apron was about 1 inch shorter than the apron on my old South bend (7" vs 8" between the bolt holes to the carriage). Apparently South Bend either made the carriage longer or shorter sometime during the life of the lathe. The half-nuts from the E-bay'd apron fit my old apron perfectly, so I am running, and happy, and have a back-up lathe again to use when my other lathes are holding workpieces I don't want to remove.
So this is a heads up for you South Bend users. E-mail and ask for a couple of pertinent dimensions before buying lathe parts.