Exhaust systems for 81 & 82 are NOT exactly the same as 83.. I bought an 82 Left and it would bolt up to head and frame correctly, but would not mate the crossover to the right. I had the muffler shop make caps, but I could have cut short and added a flex pipe. if you go to goldwinginfo.com you can figure this out from their parts diagrams.
The parts will mostly interchange, however you may find you have to change part of a larger assembly to fit the part you want to swap. For example to swap the rear wheel you will need to swap the swingarm but either final drive will work, though the early final drive is a better ratio.
If you're thinking of swapping motors the transmission ratios are different.