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You know a truck and a car axle aren't the same right?
Spring type (leaf or coil) and mounting location, axle length, backing plates, brakes, drums, axles, wheel lug pattern, companion flange etc. several variables. There were lots of trucks made from 73-91 which will bolt right in. No need to go Frankenstein unless you are building a custom setup, then who cares at that point.
You asked how the Axle's differ. Don't get terminology confused:Axle (whole assembly), Axle shaft -drives the wheels, Differential (carrier, differential gears, etc), final drive (ring and pinion). So yes, they are external differences. If your goal is to source used internal parts then yes you can try and gut another 10 bolt.