Here is the video tapping the top tube for filler neck.
This is the original drilling and tapping it was over 15 Min's long I have cut it down and here it is the actual work that was done.
YouTube - Felt Twin Drill & Tap Top Tube Edited
This video is the first video posted and was take #2 and there was no drilling or tapping done but it explains what was done much of what was in the original was cut out so with the two together it fully explains and demonstrates the process
YouTube - Felt Twin Top Tube Fuel Tank