Changing Table to LBGE Table Conversion

So, I'm going to convert this into a LBGE table.

The whole top part is coming off and the "shelf" upon which the LBGE will sit will be immediately above the bottom drawer on the the left (the top two drawers and framing are going to be cut out.

Here's my question(s).  

First off, I need to build a support structure to support the LBGE.  Starting with the shelf, how sturdy does this need to be?  Will a shelf comprised of 2x4s work or do I need to worry about undergirding with some sort of metal bracing?

Second, I will be able to use most of the existing structure of the table, I think, so I should be able to avoid having to basically insert a structural skeleton just for the LBGE.  I'm new at this kind of conversion, though.  What are people's recommendations for the best/strongest way to marry the new shelf to the existing posts?

Thanks all!!