All '63-'64 Corvette diffs used Dana posi units, which were prone to breakage, and had 17-spline pinion shafts; from '65 on, all Corvette diffs used Eaton Posi carriers and 30-spline heavy-duty pinion shafts. The one you installed (based on the stamped code) was built on March 6, 1963 as a 4.56.
Thanks for the info john, the one I pulled out is a spicer, It has a CB 9762 . with 336 gears. I have a low serial number car. and the CB 9762 seems to match the build date of my 63. So where did the spicer come from. I just retired two years ago , so Im getting back in to my vettes. Thanks again John.