Here is a page from the parts manual,
http://chevy.oldcarmanualproject.com/parts/1929_54/400.htm , and as you can see, the length is 47 7/8" just as you measured. I measure an old one I have and it to is 47 7/8" long tip to tip. I am not sure why they would be selling the longer shafts since most will want them for 1/2 tons. I found a NOS shaft front a COE and just cut off the top portion and replaced it with a top piece from a '37 so my horn and steering wheel would still fit. It's easy enough to just cut out a section and have it welded back together if you can find a longer one in good shape. The internals are all the same other then in 1942 the roller ball diameter and count changed. '42-'46 are the same, '41 is one year only, yet the design is very close.
You would hate to cut into a $200 part but that may be you only hope. Does your current one have a bad bearing race? Mine did and all the machinist I talked with said it couldn't be repaired.
