Do a google search for C-Rok engineerings 85 XJ. It was in 4wd and sport utility a year or so back. He has done what you are asking about frame rails. True it is an XJ, but the concept is the same.
Here is his shop site.
http://www.c-rok.com/
The motor trans dropping out of the bottom is a good thing. It absorbs the impact of a colision. It is designed to use the mass of the engine/trans/t-case to absorb the force of the collision and direct it away from the drivers compartment.
If you hit something that hard, you have bigger problems to worry about [img]images/graemlins/smile.gif[/img]