Thanks for that Darren. With your info I managed to find an obscure web page on a portuguese site:
http://sportscar.com.sapo.pt/1_pioneiros.htm which has photos and more info. I shall post the recent photos of the track in Luanda and the MGA as soon as I finish this trip (I am up the West African coast at the moment). I shall write to the guy that seems to own the site I found, maybe he has more leads. It also appears that it was not an Englishman that crashed a Porsche killing himself and some spectators, it was Andrade Villar - a wealthy Portuguese farmer and entrepreneur who lived in Angola since his young years who was driving a Porsche Carrera 6 in December 1969. In those days the race was through the streets of Luanda. I shall have to try and map out the course but there is one part which cuts up the escarpment (below the present US Embassy) where they still occasionally run hillclimbs which must have been hairy in the extreme!
I need to get the names of the racetracks clear. The Restinga is the name of the long bar of Lobito, just north of Benguela which would have made it a street circuit. Did Benguela have its own circuit? I suspect it did. The Fortaleza is in Luanda (a fort on the edge of the escarpment but did it give its name to the Luanda street circuit as opposed to the Autodrome south of the city?). If you look at the photos on the web site of the start of the Angolan grande premio, you will see the fort in the background.
My thanks also to Klaus. Several years ago, obviously while the war was still going hammer and tongs, I heard of some Portuguese guy in the interior who swapped his brand new 4x4 for some old car he had discovered but I could never find anything else out about it (it was probably spirited away!).
This is all proving very interesting as I continue to be surprised at some of the exotica that once thundered through the streets of Luanda. I shall press on and keep you informed of anything else I turn up.