If the pot is the 'typical' type you get with turkey fryer kits (very thin aluminum) you most likely won't be able to put a valve on it. The 30qt pot that came with my turkey fryer is this way - the metal is just too thin to support it. If you could find someone to weld on a relatively large curved plate to reinforce it then it might work, but at that point (unless you've got a buddy that can do it free) it would probably cost you more than just buying a higher-quality pot, and/or making a keggle.
The burner is fine, it sounds about the same as mine, and I have no problem bringing 6-7 gallons to a boil in a very reasonable amount of time, and keeping a good rolling boil without having to keep the gas anywhere near to fully on.