Q: spark plugs and cables

Ok I bought the truck bout 2 years I know it doesn't have a lot of miles on it, but it looks to have original plugs and cables I went to the parts place and askes for spark plugs and cables. I got Motorcraft spark plugs cables, and Motorcraft double plats. The problem is no one there knew what the spark plug gap was supposed to be. They had 3 different gap size plugs in different brands, but they only carried 1 gap size for the Motorcraft which was 0.044. Ok i got home looked in my owners manual, it has a range of 0.049 - 0.053. Ok first does it matter if its copper, plats, double plats , do you still set the gap for what the owners manual says ? or do the different types need to be set different because of the type? Second , when you have a spark plug gap range of 0.049 -0.053 what do you set it at? The low end of that range mid or high. What should i set the gap at?

My car has 84000 miles.
My car has an automatic transmission.