Things to look out for:
- has it been ridden/serviced regularly, or standing for a long time?
- ride it! Go hard in second gear - if it pops out of gear don't buy it.
- find a good straight and run it up to almost red line in the first 3 gears at least, making sure it runs properly throughout the rev range.
- with such a low mileage, there's a good chance what you're looking at spent a lot of time standing, and that brings on a lot of problems, especially with carbs wear and deterioration.
- while you're shopping, have a good look around. There are many newer ones from the 90's going for very similar prices. You should not pay much more than $2500 for a pristine '85.
- when you ride it, make sure you're upright when hitting the vboost (6000rpm and up), it's a lot of power.
Bike got upgrades all along, newer digital ignition in 90, bigger forks and front brakes from 93, and all the best small engine things etc from 99 onwards.