Question
I WILL BE RUNNING OUR DRIP IRRIGATION SYSTEM @10psi gravity flow we are using drip tape that assumes 1/2 gallon flow per100'@10psi we will be installing 2100'drip tape per section. will a one inch header pipe be adequate to supply 7 300' runs of drip tape? header pipe will be 65' long supplied by 2" main

Answer
Remember that you will have a lot of pressure loss due to friction of the water in the pipe, so I dont think you are going to have enough original pressure to operate your system, no matter what the size of header pipe.  You may want to consider a small pressure system.