Have your machinists cut the side out a 11/16" socket (clearance it so it fits) Put the cutout side toward the bonnet. Douche it in penetrating oil and maybe a couple of love taps....
You know, if they are as rusted as you say, trying to break just the nut off might take the stud anyway. How easy is it to replace the stud? When Dad worked on heavy machinery, he found it easier to just snap off the 5/8" stove bolts that hold grader bits on than trying to remove a bolt that it rusted and packed with dirt. Granted, these weren't studs that you'd have to finish digging out, but still....
Have you tried a GOOD, TIGHT combination wrench?
Catchya on the Flip Side -- Have you RTFM? I'm sure there's an official tool
