It will need to be custom but you can typically use parts of a stock crossmember.
The only thing that I can say is to get the drivetrain sitting at the hieight that you want it and see what you can do. Every vehicle is a bit different.
This is a picture of Wallys crossmember. It is for a reference only. The way it works is that it bolts up to the inside of the boxed frame rails with hidden welded in nuts.
You can see the center cross bar is a piece of 1.5" X 2" or so square tube. Wally has an old school steel doubler so we did some other things for bushings to mount it but you get the idea.
The piece of 1.5" wide tube will fit between the cases and use a shelf off of the front of it to support the mounts with some bushings to the bottom of the adaptor.
The pic below is a picture of Fox's 4X4 iron/ORD modified crossmember. Pay attention to the frame mounts. ORD added vertical stiffners to the inside of the frame to keep the frame from collapsing during a hit.
This is a good clean design that gives the best clearance for a normal application. You could gain an inch or more belly clearance from this but there is a lot of work involved with that.
Link to the thread.
http://coloradok5.com/forums/showthread.phpt=148678&highlight=Fox+Chassis&page=2
There are some good pics in that thread.
Hope this helps some. It's all custom work but with a few ideas and pictures I think you could use some stock crossmembers and a little thinking to have a nice clean design that works well.