Having been an inspector myself I will say it is entirely possible (likely even) that the other shops are not inspecting this feature at all or using a half-measure just to verify it "seems ok enough" - 0.005" runout for that length is a bit over-the-top. Even if you had a 10ft CMM you'd have to...
If you want to make your drawing needlessly ambiguous and confusing (in practice hardly any inspector cares about GD&T) then go ahead and do it like you've shown. I tend to prefer simple and obvious.
If using a CMM or similar, you would do your initial alignment to the A plane, then set your x,y origin to the B cylinder. Then to report your true position it would be the distance in terms of x perpendicular to the midline of the slot. The maximum deviation in terms of x would be +/- half of...
