I would get angle iron and cut it like shown below. I think you will save a crap load of time. In the attached photo what you cannot see is the tab sticking out where the angle iron was cut out has about a 3-4 degree twist to match the slope of the frame. Plus those mounting feet drop the winch about an inch, and that's a lot with the tight fit, so the regular angle iron will put it a bit higher it the frame rails. If you get 1/4" iron it will be plenty strong. It's what they sell now for them, plus the mounting holes are already drilled. You can vise the angle iron and put a slight twist on the mounting cutout to match the angled slope of the frame. I thought my iron was 5/16 when I measured. but the link below shows 1/4". But you could check out Ramsey too, if you choose to go that route.
https://www.piercesales.com/universa...-mounts-ps654/
That tab is twisted to match the slope of the frame! I can take a picture of the twist ir you like. These photos are just what I took during install.
J