Take the no 1 spark plug out and turn the engine over until the piston is at TDC (or very close) - the rotor arm should then be pointing to the HT lead connected to plug no 1 - or be 180degrees out - 50/50 chance (saves taking the rocker cover off).

Clockwise from this position, the leads should be 1-4-2-5-3-6, with no1 at the front of the driver's side bank, and no3 at the front of the passenger's side bank.

Don't make the mistake of connecting your HT leads in the same position as on someone else's engine - their dizzy may have been put in in a different orientation to yours (the LT wiring plug on the side may be in a different position).