Tractor Repair: I.H. Tractor, timing light, tractor engine

Question
Could you please outline the correct procedure for setting the
timing on a 240 I.H. Gas engine.  I am getting ready to pull the
head off the engine for a trip to the local machine shop, due to
a broken off manifold bolt. Any information will be welcome. I have never pulled a tractor engine apart but have built several
car / truck engines.  Thank you in advance.

Answer
You shouldn't need to retime it after removing the head, but I think there is a timing mark on the front pulley.  The distributor should be turned so that the number one spark plug fires when the mark lines up with the pointer.  Some people time them by ear, others use a timing light which is more accurate.