Motor Mount replacement

I need to drop in some new motor mounts with the motor in. My haynes manual says you can but I've run into a problem.

The mount bolts don't want to thread out of the frame. They spin and spin and spin but they aren't backing out.

Are there nuts on the inside of the frame?

If so how can I see them and get to them?

These nuts aren't supposed to turn are they? I would think that if there were nuts inside the frame, they would be welded in place.

Maybe there aren't any nuts, maybe the frame is tepped with threads? If so, how could the first three nuts strip so easily?

Help! Please.

i'd have to crawl under mine and look to be sure, but if there is a nut in the frame, there should be a hole to access the nut from.

the book i have says to remove the through bolt, and then unbolt the mount from the engine. it doesnt say to remove the piece from the frame.

The motor mount on the frame is not accessible from under the truck. My 84 had the same problem and I think there are nuts welded inside the frame. I cut mine out with a cut-off wheel and drilled holes underneath so I can get to them next time.