My pleasure Janey... I don't have a 66 yet -worst luck- but I keep the link in case I have to change the presser bar on any of my existing machines... .. I don't own a 27, only 28s and one 128, they have one screw too but I imagined it was only because it was smaller...I think the part where she explains how to align the bar and feet can be useful for the 27 too.
And good idea using the "dirt marks"!!