I had occasion to chop and channel a set of TF/BC era steps.
I found cutting along the edge of a corrugation valley or ridge rather than the middle of a valley or plateau made things much easier.
It's easier than patching in a large flat panel, that's for sure.
So I guess I'm saying find another trashed running board with enough good metal to work with and don't concern yourself with 'If it's Right' from the supplier.

Give me ambiguity
or give me something else