Quote:

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This is a pic of the installation so far, where the X member will sit, strong against the frame comnnector, and barely clearing the exhaust....

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Myself I would move your cross bar back so its just
in front of the holes in the brackets... with what you
show there the brackets will have too much leverage
on the tube and will twist it if not tearing it right
out... you would like the bars to push up at the
bar or under it so it applies the load directly
to the bar
EDIT
The applied load will vary some based on the bars
angle but the applied load will be about 30* to about
40* from the horizontal