JLT, I tried to do what you said and stick the cross member inbetween the frame rails. This did not work. It does not set flat on the frame rails.
I could put some kind of spacer to get it to set right, but in the end it would cause my transmission/transfercase to be to high.
I am just going to mount it to the bottom and run some 3/4" spacers between the transfercase mount and the bushings. This will allow me to be right in line with the stock mount for my carrier bearing. I will not be 4x4ing this truck hard at all so having the cross member that low will not effect anything.