if it is only two holes you could simply call out surfaces in each of the X, Y, And Z planes, preferably surfaces that are geometrically important to the mating parts, and use the true position callout for each of the bores referencing the three datums. if there are more than two I would locate one of the holes using true position to the three datums, designate it as a fourth datum and locate the other holes true position to all four datums. this allows the hole pattern to shift as a pattern, but the holes remain controlled and located to each other. doing the same with a paralell callout (or even with non-GD&T tolerances for that matter) would result in a square tolerance band instead of a round one. true position is by far the better way to designate this.