[1963c-10]

WA is a non posi 3.73

WC shows as the 3.73 posi code

Best thing to do is pop the rear cover and verify. That will definitely let you know posi or non posi and what gears you have. The gears are stamped on the sides. The rear end may be a 64, bt you don't know whats inside unless you pop the cover.

1st Pic for reference posi unit....in this case you see the part # 3862691 and 14-43 for the gear size. Divide 43 by 14 = 3.07 gear
2nd pic for reference non posi unit #3862525 11 41 would be 3:73