I've just built a system for a friend using a TX3 CPU cooler and the cooler can be mounted horizontally or vertically.
It is best to mount the fan so it blows air through the fins, but it also is possible to attach 2 fans on a TX3 to operate in a push/pull configuration.
I am now considering using a TX3 on my 955BE system with a duct to draw in cooler air..