Ditzler, as you most likely know, is now PPG.
Check out the Tech Tip here regarding 47-55 paint codes. In that Tech Tip is information on how to contact the PPG Color Library - they have always been able to provide a modern code/formula for exterior colors for those years.
You say no one could give you a modern formula/mixture. Did you try the PPG Color Library (not the local PPG dealer/jobber)?
With regards to amount of paint, my experience has been that it is somewhat hard to judge because different types of HVLP systems produce different amounts of waste/overspray. My Accuspray turbine system uses 1/2 to 1/3 of the amount used by "conventional" spraying.
You question is important because you no do not want to "over buy" very expensive paint.
