The bore scope isn’t giving much info because I think you’re seeing the smooth case rather than the side gears in that shot. You need to double check that your knuckles are installed correctly and that the axle shafts are indeed inserted into the side gears in the differential. Sometimes when...
If the hubs are in the free position when you have 4wd engaged the differential will not engage the axles. Lock the hubs and put it in 4wd. Put the transmission in neutral and then see if the front axle rotates as one unit with the drive shaft.