I have an '81 R80G/S.
After my first trip (Melbourne to top of Cape York, about 800km corrugations, creek crossings, etc), I *hated* the bike.
However, after much work, I improved it, and spent 18 months travelling with wench on the back around Australia.
I now *love* it.
* throw away the stock forks.
I fitted Yamaha TT600 forks, requiring a custom steering spindle.
The stock forks are too flimsy, and don't offer enough travel.
* Make the final drive breathe.
Otherwise, first bit of water, and voila! it's full of H2O. Replace the top breather on the drive with a tube connector, and run a rubber tube up into the air box (with a loop above, to stop any diff oil running into the air box).
You should probably do the same with gearbox, which loves sucking water.
* Re-route the engine breather.
Normally runs into the air box, and spews oil therein. Just run it *through* the air box, out to the ground.
* Fix the million & 1 electrical problems.
eg. rewire the alternator to start charging at lower RPMs.
& replacing the wires that broke going to the instrument / switch up front.
* Replace the gear & chain-driven throttle mechanism.
ie. the one on the bars.
If run for some time with a dragging cable, the gears can wear out, resulting in little, then no, pulling on the cars.
I rode from the top of Cape York back to Melbourne (4000km, odd), having to pull on the cable by hand. I couldn't get the right parts at the time.
I replaced it with a "conventional" cable pull off an old Suzuki dirt bike I had.
The main thing is to remember that you're on a bloody big lump, which *will* go most places, but needs some respect.
Cheers - Gavin.