another push rod question

Well here I am asking for help yet again. I am measuring for push rods but I am not sure where the set screws on he rockers should be to get the correct length. Currently I have them set all the way in and the average measurement with is 6.75" or 171 mm. This is on a hrd roller lifters in a 340. Should the set screws be set all the way in? Also, where is the best place to buy push rods?