Making progress and just discovered another interference:
The under bed spare carrier brace is occupying the offset hole (aligned with the 5th side strip hole from the front). I added the carrier according to the FAM . Perhaps the two can share a bolt?
There is another similiar hole a few inches further down, close to the frame crossmember, I could use. But then the wood bolts on the cross sill wouldn't' line up.
Or, move the spare carrier further down the frame?

EDIT: Moved the spare tire carrier towards the rear of the frame. All is good now!
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Last edited by Nhluvstruck; 08/09/2018 1:20 PM. Reason: Updated progress.

NHluvstruck...
1951 3100 5-window,.sold, regretted
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