I have no idea what the precise dimensions are, I have always used the following method:
1. Park car on a flat surface as close as possible to a wall or garage door.
2. Make a chalk mark exactly opposite the centre of each lens
3. Reverse the car back 15 feet or so
4. Strike a vertical chalk line through each spot, and a horizontal line that goes through each spot
5. Adjust the main beams so the bright spots are on the centre vertical and just below horizontal
6. Check the dips throw the light to the left and below.
It's probably wrong, but I've never failed an MOT yet on poorly adjusted lights. You could probably spend ages on precise adjustment and get a better throw up the road, but I don't drive fast at night, there are two many animals to look out for.
Remember that on the traditional 7" bowl headlights, you shouldn't have to touch the adjusters to get the retaining ring free, it's held by just the little screws that go through the flange pieces with the cutout. Slacken them off, and you should be able to twist the retaining ring free. Dosing all the threads with ACF50 is a good idea.
