For 48 the axle serial number would be located on the top of the carrier housing. For two speed on top of differentail carrier towards the rear and right. ratio standard single speed 6.17. Two speed 6.13 and 8.10. School bus option could be either6.13 0r 5.43. I didn't see anything on how to dechipher the numbers to indicate how it was equipped, that may be covered in the owners manual.
