Ford Model A - Oil hole for rear camshaft bushing

My engine is an early 29er model and has no oil hole at the rear camshaft bushing. In the 'Model A Ford Service Bulletins' is described how you can add this hole correctly. This is a modification which was done also by Ford in former times.

This is the hole where oil can run from the valve chamber directly into the rear bushing.

To get a hole at the right position I used an old bolt and filed a notch on one side. All details are described in the book mentioned above.

The notch acts as a guidance for my long drill to make the hole with the right angle. Source:  http://www.maurer-markus.ch/ford_a/mod_nockenwellenlager.en.html