One piece goes from one side of the tank, all the way to the other side, starting and ending at the rear edge of the hood. At the sides, it runs between the cowl and the tank, and in the center, between the tank and that filler strip that runs right under the windshield. There are various tricks for getting the welting to stay in place. You will need to pre-cut holes or slots for the bolts that hold the filler strip and tank to the dash rail. You will also need to make some notches in the flat part of the welting to help it go around the corners.
I think Marco has a detailed photo that shows how the front end of the welting is finished. The last inch or so, where it passes under the cowl band, has the core removed, and it serves as an anti-squeak under the front top corner of the cowl.
Doug