I'll go with Oldsub on this one. You'll want new wireing for sure. You might be able to use some of the air conditioning parts, like the compressor and the condenser, but the wireing should be replaced with new.
On the axles/t-case, any reason you want to change them? I'm suspecting that it's for a better gear ratio, right? Installing them into your existing chassis shouldn't be much of an issue, they're very similar. You will need new driveshafts as the later t-case is not the divorced type like the original. 1 thing to be carfull of though, 1-around '81 was when GM started to use lighter duty axles in their 3/4 ton trucks, it could very easily have the corprate 10 bolt front end and the 9 1/2" semi floating rear end. Not that these diffs are waek, they're just not as strong as the earlier Dana 44/ 14 bolt full float combo. Especially if you plan on running large (over 33") tires.
If it's a heavy duty 3/4 ton, that's much better. They have the full float rear and the Dana front.
