I forgot all about the 4.7s and sludging issues. Not having one, Ive never had the issue. Installing a mechanical oil gauge is not hard. You would simply (temp) take out the oil sending unit and screw in the mechanical oil gauge in its place.
IF you do have sludge and IF you want to clean the internals WITHOUT tearing the engine apart then there are products out there that can do it. Marvel Mystery Oil, Seafoam, some guys use diesel. But BE sure you follow the directions and change both the filter and oil afterwards.
I have used diesel before myself and had great results.