Need help modeling ramp-like side on a special hinge part

[derei]

I'm trying to remodel this http://www.southco.com/en-us/r6 (the step file downloaded from website is very messy) but I have some problems with a ramp-like side of the modeled piece.
I could just slice it diagonally, but if possible, I would like to have it as the original part is.

Thank you.

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Hinge part.skp

[pilou]

Curvishear by Fredo 6?

Careful plugin generates only curves!
You must use Curviloft (or others) afterfor have surfaces!

(in the image top left corner, the 2 curves are the curvy curves! )