Very interesting. I own 4 dana 41's (only 2 are attached to a truck). All 4 have the following: "W 41/11" (3.73). One is a 49. One is a 50. Other 2 are unknown year. I wil say this, mtflat pointed out that the shop manual had a misprint and should have said 3.73. But that doesn't explain this particular rear end.