Take a tape measure and measure from the axle flange surface into the bare housing to the center of it(eyeball it ) , if your using a spool. If your using a posi unit measure the width of inside the posi on the splines on each side to determine how far apart the axles end will be in that posi unit installed and then install the axles in the bare housing and see how much width is in between the axle ends
I have had to cut some off the splined axles ends off when switching axles from one housing to another to make sure the axles didn't butt up against each other in the housing using the same spool in both housings
8 3/4 axes are the same length on both sides, do NOT swap a used axle from the passenger side to the drivers side, DO NOT reverse them from one side to the other
Most Mopar Dana 60 axles are shorter on the passenger side than the driver side in cars, vans and pickups
Did you mark or do you know how to tell which axle was used on the drivers side and passenger side If not try and figure that out when you reuse them and install them on the correct, original sides
Good luck on figuring these issues out