i have only one thing to say... box the frame... it takes no time, looks better and adds torsional rigidity like NO bolt in contraption ever could... that frame in that picture is from an engineering standpoint so wrong it makes me want to cry... there are no triangulating structures, the framerails are torsionally far infrrior to what a square profile with simmilar external measurements would be... do the math if you dont believe me...
so box the frame.. and if yoy really want to add a bolt in structure.. make it an X instead of that bedframe you posted....
heer is a pic of my frame... it really isnt that big a deal... it can be done without removing the body!
also, stiffer bodymounts are worth considdering... mine are aluminum so prety stiff :-)