Something like this then? Kev should be best person to write these sorts of things. I reckon he could write a whole encylopedia of mini tech. NOW THAT'S AN IDEA!!!
Buying the alternator
Look around for the best price on a Bosch N13 Pulsar alternator with some sort of short term warranty (plug it in, if it doesn't work return it will do). Make sure it came from a Pulsar and not a Ford as they are exactly the same but the bottom bracket on the Ford one sticks too far forward and won't fit behind most roundnose grilles.
If you go to Pick n Payless type spare parts places, make sure you also take/ask for the plugs that go with it. The main connection that goes to your ignition coil and back to the battery requires a (bigish) 5/8" fork or ring type spade connector, and the lights/starter connector needs special plastic plug thingy. You can do without for the later, but it's messy as you have to use regular spade plugs.
When you buy the alternator, try to bring your old lucas one with you to compare. Most likely pulley on the Bosch alternator is offset and has a spacer between the alternator housing and the pulley then it may not line up perfectly with your current fanbelt. If possible get the shop to loosen this nut for you, which will save you having to clamp in and undo it using an allen key and a wrench later on.