Can you share some pictures. When you say wiring harness for locker device, did you get a REMACK with a inter-wheel differential lock when the original one did NOT have a inter-wheel lock? Did the original and REMACK have a inter-axle differential lock.

When you say installing axles, I am assuming you are intending to say axle-shafts. The Left Hand side (Driver side) axle-shaft for diff. lock has longer spline but if your original version did not have a diff. lock and the REMACK version has a diff. lock (assuming it came with diff. fork and clutch), you will need to slide in axle shafts in a specific way to go across diff. clutch into the side gear of the differential. You should be able to use the REMACK carrier with the diff. lock on this truck.