Jim....aren't you asking this on the wrong board???
If you were to do anything like that, I'd use a serrated mounting "slider" setup (think dirt track/oval track PHB setups). With the loads on that joint, I'm afraid it might not stay where you put it. I'd probably do as Rob and Jon did and drill the holes you need (you may need to weld on a doubler on the outside to give a place to put the holes).
Just my thoughts.