This evening after installing the sender on the second most outboard rib, I got Anne-Marie to give me a hand dimpling the left fuel tank skin. Next step is the fuel cap and fuel drain which need to be back drilled and countersunk. The trailing edge of the fuel tank skin where the rear back plate goes will be machine countersunk, so I had to resist the urge to dimpel this area, I guess it causes too much distortion of the skin and hte back plate and might result in a poor seal.