If no one has an answer, it's easy enough to measure yourself. All it takes is a head, a valve, a spirit level and a machinist's protractor,
Slide one valve into one of the valve guides and use a piece of tape or something across the face to hold it closed
Set the head up on a table and level it with the spirit level and some shims
Put one leg of your machinist's protractor on the valve stem and set the other to dead vertical with the spirit level
Read the angle off the scale