you have to cut a hole in the floor to access the capture nuts inside the floor support...and then weld them securely in place.
Too late now but, you should have drilled small holes in the floor (directly over the nuts) and soaked them with PBlaster for a week or two.
If you don't have access to a welder, there is another way (actually there are lots of other ways - this is just one).
1. Cut the bolt where shown:
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You want the part of the bolt that remains inside the floor support to be short as possible.
Use a step drill and make the biggest hole you can directly over the square nut. To locate it's position, you can:
1. Drill a series of small pilot holes and a flashlight
2. Use a tape measure from underneath and then inside the cab
3. Use the pinch weld marks (and the dwgs below) on the cab floor as a guide:
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When you have a hole in the floor, pull the nut (and the attached bolt stub) up into the floor support and shove it aside. Renew your bushings.
When the new bushing stack is in place, install the through bolt from the bottom. But this time, instead of threading it into the original square nut, just use a regular nut and the biggest washer you can fit through your hole. Drop them in from the top and onto the bolt, hold the nut with a pair of needle nose pliers and torque the bolt from underneath.
Paint the raw steel made by the step-drill and close the hole with a standard rubber plug.
