I would increase the angle up to 45 ish and make it wider. Best look at it with the full image not just the top part, the lack of height above it is misleading.
Just a standard Lancaster type.
Making the outside corners is easy that way. I would make the diagonal pieces in the corners with an English Wheel now, better curve that way, mallet and sandbag for the first shape and EW or Planishing hammer to smooth things out.
The triangular reinforcements are mounted inside the rocker. I believe they are used to strengthen the rocker where the steps are mounted. You can see how to make them on my Rebuilding a 40 in a one car garage thread, page 17.
if you click the link in my sig you are there.
Its always better to come to that conclusion by yourself.
btw, you know the More you do the further you are willing to go, ask me how I know.😏
there is always more rust to Tackle.
I use the English wheel to stretch the ribs before I bead them in. This helps with the distortion after. Especially when there is bending After it limits the amount of shrinking.