So are you running a RIM heating setup? I would assume so with the inverted keg. Like you mentioned the Guinness keg is only one of a few that is threaded. So if anyone looking to follow your design you need to check out the keg you want to use.
Craig
I was for a while, but grain was getting stuck in the chamber and getting burnt on the heating element, had to completely take it apart and spend an hour cleaning it, so I just started heating from below, it don't take much to maintain temp only if you want to raise it significantly. when I mix my the water and grain, I calculate the strike temp of the water so when they are mixed I reach 152 deg. and then I just maintain with a small burner, and once you do it a few times repeating it is real easy. I am working on making the stainless chamber that housed the electric element into a flow through design by wrapping the outside with some High-Temperature Heat Tape, you need about 1200 watts to maintain temp, so I'm still looking for the right stuff, but until then this is working great.
The Guinness keg was a real find, the thread is some bastard European pitch that I could not get any of my American or metric pitch gages to fit, so we experimented until we matched it up.