Gday mate this is the link with that other build idea.
http://www.jeepforum.com/forum/showthread.php?t=776123
He used 50x50 angle welded to some bent up plate for the skid, and 50x100 to make the crossmember but bolted it to the chassis.
I don’t like the drilling into the chassis idea he done so…..
I am thinking if I use your Gearbox mount modification idea
and make up his 50x100 crossmember, But weld that to the 50x50 angle and bolt it all up to the existing 6 bolt holes in the chassis for the STD skid plate.
Then welding strong tabs with nuts to the crossmember and angle to bolt the skid plate up.
Hope all that mumbo jumbo makes sense