There seems to be a lot of help with this, and if I should repeat what someone else says - then it is just reenforcement.
On my body, there were gaps intended to allow the builder to place hard rubber strips put between the body and frame.
AND, there was an inspection of the body sitting on the frame to check those points intended to be frame to body contacts.
These are points I would have when I started to put the body on.
Mine took 9 people about an hour once all of the prep work was done.
It was turned 90 degrees to the frame and lowered slowly to see what was "in the way" and what needed to be welded/changed or cut off.
Hope this helps and good luck.
