Before Mersin -> Egypt came on the scene (i've lost track with that one) I recall reading about Turkey -> North Cyprus then Cyprus (N or S?) -> Israel and from there overland -> Egypt and so on.
Reading your OP I would drop Morocco and Algeria - great in their own right but not worth the expense/bother just to tick off all the North Af coast. Instead ferry Genoa-Tunis (Tunisia is no prob), do the Libyan border near Nalut, organising a helper there at least, if not an escort right across.
As Cam J says elsewhere:
The biggest threat facing visitors to Libya is the driving habits of the locals
so your 80s despatching skills may come in useful + of course keep your wits about you in general.
Egypt crossing had streamlined a bit I was told. Need to return number plate or get something cancelled in last Libyan town back from the border. From Egypt proceed as normal.
Ethiopia visa: if it doesnt work in Cairo get it in Khartoum. Ethiopia might get shaky with the recent death
of the hardline PM, but you cross that bridge when you come to it.
Back home it's easy to contemplate add-ons like Somalia, but unless you are a very worldly traveller I suspect by the time you get to Ethiopia you may well have a plateful just keeping up. Peace may have broken out in Mogadishu and good luck to them, but that's one shot-up capital in a big country. What does anyone know about overland tourism there - no one's done it for 30+ years.
Suppose I will need to contact the Embassies in London rather than getting visas on the way - which means less flexibilty.
Tuni - Not needed
- Organise in UK, see other posts
Egypt - Needed now, right? Get in UK
Sudan - Get in Cairo
Eth - Cairo or Khartoum
And from Kenya south they're all border jobbies apart from Burundi and Moz, afaik.
PS: I see you just ordered the book. You will actually find it useful for trans-Af routes + by the time you get it will be a better departure time anyway.