Scott,
Sorry for the delay in answering, been camping. In the bottom rendering the tongue stops short of the axles. I don't believe you can weld to the torsion axles, you would melt the rubber inside. Dexter says to bolt the mounting brackets to the axle, locate the axle and weld the brackets to the frame. I would probably be careful to watch how much heat got to the axle tube. I suppose it is possible to weld the tongue to the brackets. Never installed one so opinions may vary. Dexter's Application Manual has a lot of great information.
Jim
Application manual
http://i.b5z.net/i/u/1080235/f/Applications_Manual_Complete_Catalog.pdf