This is a picture of of the top of my tank during restoration, 28K never out of the car. The tape in the picture while not shown in the AM, was in my opinion the same as used on the fuel line and ground strap rubber cover. No pictures of that part of the tank. It was thicker than regular masking tape. I used 1" wide "Freezer Masking Tape" to replace it.
There was also the number 26 printed on the tank which was probably a mill mark for the steel.