I was able to add packing foam to the bottom of the tank compartment to raise the tank to the top of the hatch. I also enlarged the hole in the firewall to allow the fittings to go through. You might need to lower the engine too. I got mine down as far as reasonably sensible. (Some cutting of the sides of the fuse was necessary.) This will get the tank fuel supply line about 1/4 lower than the needle--this is close enough for without noticing any in-flight differences. Once your finished fuel proof the intire tank area, sides of the fuse and firewall.
Be sure to check your tank for leaks if you develop a problem. Remove the tank and put the hole thing under water. Seal the tubes and squeeze that thing to see if any bubbles appear around the seal or other places.
Double check your clunk to make sure it's clunking correctly.

This should take care of the problem.