Newbie with '29 RPU

[cdnwillyg]

Hey forum new here and the new owner of a '29 RPU in need of some love.
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I have this issue on the rear quarters where it meets the cab floor and don't know what I need to do? Its the same on both sides. It looks original but after 95 years thats only a guess.
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I should mention there are no body wood blocks in yet so body is sitting directly on the frame.