Yes.... They have little cells in them (think NCR Carbonless). I just did this at work to diagnose a sealing problem on a machine..... Worked like a champ....
I have never seen or heard of the trick on intakes since I saw it myself but it is a useful and simple way to check to make sure the port are properly aligned for fitment. Mine was off minimal but he took the information he obtained from that test and milled the intake for me that evening. Problem solved which is very similar to yours. My motor was more of a Race Application but none the less a similar problem...
The guys name was Dave Barbarian and anyone in the Richmond area who knew about Hoenes and Eanes will know the name. He was crazy smart and was killed in an automobile accident back in the 90's.
