I believe Rolex used a number of differen types of radium compositions when they made these pre-tritium dials. I think not only did they use different radium compounds (which is documented) but also they varied teh amount of radium applied to each dial (also documented).
What i find interesting is when certain vintage Rolex dealers try to make claims about authenticity based on just a Geiger reading.
Only two types of people would do that. An idiot or someone with an agenda.
My point is, I have seen quite a few 6542s in totally original state that have varied radiation readings. To my mind...anything between 0 and 400 microsiuverts is totally possible.
Though to be fair, i would only wear one with your level or lower!