If a guy keeps looking down at his own body when talking to a girl and has other positive bosy language, is he willing her or guiding her to look at him? What about an upward nod when leaving a group that seems to be directed to her?

If he keeps looking down, it's probably because he's shy and can't look at you in the eyes.

If a guy keeps looking down at his own body when talking to a girl and has other positive bosy language, is he willing her or guiding her to look at him? What about an upward nod when leaving a group that seems to be directed to her?
No, if he keeps looking down at himself, he sounds shy or unwilling to make eye contact. If he were trying to impress you with his looks, he'd smooth his hair a lot, make muscles in his biceps, lightly pound or pat his chest occasionally. An upward nod could mean "I'm too good for you" or "Who do you think YOU are, babe?"

On the other hand, an upward nod towards her when leaving a group could mean - "see ya", directed at her personally. If there is eye contact with the nod, then this could be interpreted as flirting.