Thanks for that, it had me a little perplexed for a while.
Do I base my distributor position on the idle speed I obtain? At the moment it's ticking over just under 1,000 rpm (just as a test) whereas before it was at the more normal 800 rpm tickover.
If I don't set it by the idle speed, is there a more 'scientific' way to set it? Again in the manual I have, it states there is a marking on the machined face at the top of the distributor body, and that this should be aligned with the rotor arm. With the metal contact of the rotor arm being about 0.75 or an inch wide, and the marking they refer to being a scribe line, there's plenty of room for error. (I'm also starting to be more than a little sceptical about what the Haynes manual tells me!)