Strange.... WS along with the date code (August 26, 1969) and the heads (#12, August 7, 1969) all match up for RA III. However, The ground and re-stamped last digit on the block casting number is consistent for how some RA IV's were built. Now I'm really curious to find out which cam you've got. Right now, I'm leaning towards the following explanation:
We already know that RA III and RA IV blocks were identical except for the numbers, and "running short of" RA IV blocks is the explanation commonly given for the re-stampings. However, keep in mind that the factory cared about getting the cars built and not interrupting "the line". They didn't care so much about making everything match perfectly, numbers wise. It's plausible that on this particular engine, the car was supposed to get a RA III but somewhere in the process someone happened to pull the "wrong" block (one that had been re-stamped for a RA IV car) but by the time the error was discovered (if it ever WAS discovered) it was too late in the build process to go back and change it. Or maybe, on that particular day in that particular plant on that particular build sequence, the plant "ran out" of RA III blocks and someone, knowing they were the same, pulled this one instead. I don't know that you'd ever be able to find out for sure.
When you do get around to finding the stamp on the camshaft (assuming it's still the original cam) then I'd expect to find an "H" stamp for a RA III cam. "WS" along with the date code according to some sources say that engine originally came out of a 1970 Firebird, 4-speed, and in some circles was referred to as a "California Ram Air III". Still other sources say it was in an A-body (LeMans, GTO) manual transmission. (Always check multiple sources, there are mistakes out there.) It'd sure be interesting to try reverse lookups on the possible VIN numbers to get more information.