The portion or length of the needle above the clip slots isn't important. It can vary and since it doesn't meter fuel, it doesn't matter. OK, you've established that you have matching needles. Now you need to determine if the same amount of needle hangs out the bottom of the slide in each of your slides. Since they are mismatched slides and mount the needles in different ways, what hangs out the bottom may differ with both needles set in the same clip slot. You may need to set one differently than the other to get the same amount of needle hanging out of the bottom of the slide.