...and one more thing: It's not difficult and complicated to do as it seems to be (except that you'll not gonna feel some fingers couple hours after). Now a head I was working with is one of those "softer" and took about one and a half hour to lapp, and some others can take double time, but its cool to do something new.
Tips: Paint a top side of a head with a permanent marker. Under lapping, if a paint is gone at the one side, but not at the other, that's the sign that you're not pushing a head at the right angle. When a pint is gone on both sides, that means that a head is flat and you can go over to next lapping film. Painting should be enough to do only once, before you start lapping.
Big thanx to Vince who convinced me to do that myself and all of you others who are sharing knowledge, experiences and opinions.
Just love this forum.