Showing the distributor drive-dog off-set from the centre-line
The drive gear in the engine - remove screw (2) and housing (4), then the gear (5) can be withdrawn using a 5/16" UNF bolt (an air-cleaner bolt as used with HS carbs is eminently suitable, but not HIF). It will twist as it is removed due to the spiral gear engagement with the camshaft, and when it is inserted, so must be positioned correctly prior to insertion as otherwise it could take up any one of eight positions which will affect the position of the distributor rotor: (Leyland WSM)
Turn the engine until No.1 cylinder is at TDC on its compression stroke. Insert the gear starting with it's slot as shown (8) i.e. at an angle approaching 10 minutes to 4, and in the lower of the two possible positions. The gear will rotate anti-clockwise during insertion and when fully seated should take up a position in line with the housing as shown (9), with the slot at lower right If the slot is uppermost the distributor will be 180 degrees out when fitted.