There are not really any bug issues.
I would inspect the chrome on the forks carefully for rock damage as there is no rubber fork boots on.
Also, check the forks for straightness as I have seen a few of these conventional forks bent.
It is a bit harder to find parts for the earlier K5's but still doable.
Bounce the bike hard several times and see if any oil is leaking on the rear shock and the forks.
Watch those brakes as they should be cleaned up a bit first.
Also, check the screws in the reservoir cover to see if the heads are stripped.
Verify the kill switch works and that you can easily access it if the need arises
Get under the bike and look for repairs to the engine cases.
Open the radiator and see if they are corroded.
If you can, run the bike a bit and then check the oil to see if there is any water in it and check the plug color while your at it.
A compression check would be nice.
While on a stand, spin the wheels to see if the rims are straight, bearings are good, and check them for cracks.
Move the swing arm up and down and side to side to check the bearings there as well.
Other than that, check everything you can carefully.
Then again, you probably knew all that