I've now stripped my 2.2 engine having suffered piston/valve damage following cam chain guide failure. (posted pics a few weeks ago).
I've noticed that the difference between the old and new cam chain oil jets is that the later ones no longer have a non-return valve fitted - it is this that makes it appear that a bigger jet is in place. I've also found that it is fairly easy to drill out & remove the non-return valve - may be a fairly easy fix ?