I have same bike with similar milage. However a few years ago I treated it to a total rebuild, it wasn't knackered but I had the time and a garage to do it in.
Pulled it apart and only real problem was the teeth on the second (and possibly fourth) were slightly worn (a common fault with these bikes). I'm sure if I hadn't pulled the engine apart I would not have never noticed this, no strange noises or bad gearchanges and I'm sure the bike would have ridden ok for many miles. It was an easy fix using stronger gears (from a later model I think).
The rest of the engine was in very good condition. No wear to cams, tappetts, valves, seals, oil pump, bearings, clutch etc etc. I could have put it all back together but, well as I had the bits and time I treated it to a Wesco 620cc big bore, gas flowed head, new stainless engine bolts, new seals and bearings. I havn't needed to touch the engine since. Though I may fit a new cam chain soon, no rattles but something to do.
The 3AJ is a very very tough old bike. If it is running ok now it will easily do a few 1000k around Morocco. Just check tappetts, change clutch plates, oil and filters.
Also take spare air filters, cables, spark plug, inner tubes, fuses, you probably wont need any (except for air filter and tubes) but it's a resurance.
When are you planning on heading to Morocco, I'm thinking of going in April/May or September (on my 3AJ).
Take your bike and enjoy..
rust & dust