Yes it would be nice if they noted that .

You can take off as much as you want, some people have made them closed chamber, but I don't recommend taking that much off .

The rule of thumb is .005 for every 1 cc so .060 would take off about 12 cc . also remember that for evey .010 off the deck you have to take .0123 off the intake face to get the intake and gasket to fit properly.

You might want to get an estimate for the work you want to do to the heads BEFORE committing as it might be CHEAPER to go another route .