Dltalfa,
Unfortunately it looks like you have a seriously "frankensteined" u-joint set-up with what appears to have been modified for connection to an unknown torque tube/axle unit.
Searching the
"473539" casting number on the flange , the 1st pic below provides what the original flange was for and the original GM part number. A further check on the web found pictures of an
NOS flange (GM# 596911), which clearly shows it should only have a "10 spline configuration" as you mentioned.
If you look at the slightly edited original pic of your flange (red arrow added in 2nd pic), you can see where it appears someone has welded the u-joint flange u-joint cup retention part to an unknown torque tube 17 spline sleeve section.
To figure out further details, you are going to need to investigate the torque tube and axle for stampings/casting codes and date info to try and figure out what it actually is???
Apparently the search for information continues. Good luck and let us know when you have more info so we can try and help identify what you have.
Dan
