Yeah, no more than 2". The driveshaft can't take much more than that and getting the assembly back to the frame would be rough with bigger brackets than that. I lowered my crossmember on one side only.
Justin, that is an interesting way of doing it. I was just gonna notch the cross member and weld a plate to the bottom, but dropping one side seems like a lot less work. Hmm, gotta poke around under there when I am done with the RS.