I am sure they are talking about Numbered drill bits, not the generic SAE type of drill bits. I got a set when I needed to drill out some jets for the carb.
I have also played around with making the Natural gas BBQ into a LPG BBQ. If I remember right, I did go down 2 #drill sizes to get it to work close to right. I live at 7200 ft. I know it is not quite the same as staying with LPG and then going up, but with playing around with it, you should get it right with time.
I believe Norcold is the same these days as Weber, not wanting to help due to Libilty and fear of law suits. That is what I was told when I played around with my Weber. Good luck