I know I am late in on the subject but if you remove that crossmember without installing a replacement (such as a tube crossmember with more clearance) eventually the weight of the cab will twist the top of the frame rails outward due to the pressure on the ends of the frame stubs that the cab mounts fasten to.
This is one reason you see a lot of modified AD trucks that have been on the road a while have the appearance of the cab sagging at the front and the hood and fenders not aligning right. Years ago I had installed a V8 and automatic in my truck and cut out the crossmember and I had those results after about 30 thousand miles. The cab actually settled down on the top of the frame rails.
