I had problems with "Zinc Pest" in the side frames of one of my Williams diesel a couple of years ago.
Still had two (2) good ones on it - one left and one right - that hadn't collapsed, and used them as patterns to get a full set of new 3D printed ones made.
They worked a treat, and I ended up replacing all of the original side frames with the new 3D printed units.
Just had to spray paint them the right shade of blue - a Chessie System loco.
Maybe this could be an option if new replacement frames are not available.
Peter....Buco Australia