Balk Question
 

When and at what level of play would you call a balk on a pitcher who is moving his body to check a runner ? Head only ? Head and shoulders ?

Any time you think it's a motion (feint) to first. Other than FED, there's no mention the "moving the shoulders" is an automatic balk. The more they move, the quicker the movement, the more likely it is that it will be judged a feint.

OBR has language to the effect that, if it's borderline, you should judge whether the pitcher's intent is to deceive the runner.

This language is potentially misleading, since not all balks involve deception, and not all deception is illegal. But for borderline moves, judge intent.

illegal deception right? many legal moves to 1b can be deceptive...right?

Some deceptions are indeed legal...but quickly jerking your shoulders to 1st base while engaged to the pitcher's plate is most certainly a balk in all rule codes.