what if first measure hole -A-.
construct a point at the center of hole -A-.we'll call this the "swivel point."
now measure hole -B-.
construct a point at the center of hole -B-.
we'll call this the "tip point".
now construct a line from our "swivel point" to our "tip point". this is line A-B.
now x,y,z origin on our swivel point.
next rotate line A-B to zplus about the xaxis. then rotate line A-B to zplus about the yaxis. Thus you have your coordinate system. the MMC is put there,(i believe), if the holes in question were to have any appreciable depth. such that the possibility of the bore's having a slight skewing angle. as long as Ø's A and ØB,at any depth actually on the two end plates,is within the MMC tolerance allowed, then the part would have to be deemed good.