Welcome to the forum!
Where about on the planet do you live? There may be someone on the list nearby who could give you some direct assistance.
If it is a 1984, then it has all of the best improvements that BMW put into these bikes over the production run. A bike that has been running on the road will generally be a good sign, if it has been sitting in a shed for years then there could be some R&R needed to get it healthy again.
There is a thread on this forum where we've gone over a bunch of the usual stuff to check out- I'll see if I can find it and post a link to it for you.
How mechanically skilled are you? This will be an important question to answer if it looks like a fair amount of R&R will be necessary on this particular bike, (though if you are riding and mainting a 68 Honda then you're probably mechanically qualified!. Paying a BMW mechanic shop rate to do all this stuff can quickly double your up front investment, if it is needed.
Ask to see any maintenance logs, receipts, etc. for the bike - either private logs by the owner or receipts from the garage. Check that the odometer /speed are working and original. Depending on the mileage, some stuff may be due/critical. Give the steering head bearings, wheel bearings a careful check over. Ask when the final drive splines and the clutch splines were last cleaned&lubed - if the owner has no paperwork and gives you a blank stare, then prepare to be diving in to do this if you buy the bike. Bring a digital camera with you to take closeup pictures of things so you can examine them later (or show them to us) - I can never remember exactly how stuff looked 30 minutes after I leave the driveway.
Here are a couple threads to get you started -
http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1281119048/14#14And:
http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1273669114/0#0
