We have that same aluminum tank as well, and moving the brackets is an option that would put the drain on the bottom. Or we can get you the AccuAir tank, which has the drain port angled on a 45. You can virtually mount it any way you want, and the drain will still be functional. That is what I recommend for your application. You will pay a little more for the AccuAir tank, but it will have what you need. It might end up being the same cost if you had one modified, etc.
It is about the same physical size as the link below. The mounting is different, as it just has closed off bungs for mounts.... no "legs". Just need to drill 2 holes and it is mounted. Instead of 1/2" ports on the end, it has 3/8". Also has one more additional 1/8" port on the body of the tank, next to the drain.
http://www.azproperformance.com/3-Ga...-Air-Tank.html