swapping the axle "should" be a direct bolt in project. a dually pickup would have a rear sway bar, and the c&c's i have do not. the shock mounts, spring perches, u joint, brake lines, and e brake cables should all be interchangeable. if you want to do a srw fleetside bed with the dual c&c rear end, i believe modifications to the inner wheel wells are necessary. if you want a dually pickup rear end from this era you need a dana 70, if you want a 14 bolt dually pickup rearend you'll be looking for one from the 90's, but some fab work will be required for the spring perches and shock mounts.
assuming your truck is 4x4, since it was a fire truck if you want to go srw (single rear wheel) you want to make sure you get a 1 ton 14 bolt as the 3/4 ton have wider spring perch spread, and then you can just swap your drw front hubs for srw hubs. if its 4x2 i don't know if you can simply swap front hubs or not.
also, i think this is a given, but if tour truck is 4x4 you need to find out what gear ratio you have when swapping out your rear axle so you don't mix the wrong gears. if its a 4x2 you have several possibility's for the gearing option that will suit your needs best.
hope this helps, otis
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