I have a rear axle with the same casting number of 3725899. There is another number just above the other. On my axle it is A297. After much searching, I emailed a company that specialized in 55-57 chevy cars. This person explained that the axle was from a 1957 car. The "A" stands for January. The "29" is for the 29th of the month. The "7" is for 1957. My axle has a 3.55 ratio. It is also a non-posi.
I also have noticed that the axle is narrower than the original. However, the spring perches appear to be in the correct location. This should allow for an easy bolt in.
