You’d need to get the resolution quality and divide the projected position by the normalized quality.
This tutorial is out of date as of 4.7, now you can just use the WidgetComponent and change the new Space property to “Screen”.
I’ve just checked in a fix for the quality issue, and extended the capability to control the ZOrder of the widgets added to the viewport, for both the standard BP call, as well as the WidgetComponent. Which will allow you to control what layer they appear on LHutz. Those changes should be in github master soon / 4.8.