To me, and take this with a grain of salt, it looks like it's seen better days and I'd make a decision before doing anything. In other words if it's functional as-is what's it worth (if sold). If you keep it, how is it going to be used? If I were to keep it, it's all or nothing. I'd remove & replace all three spindles. While apart I'd have it sandblasted, weld plates where spindles are drilled for new spindles. Prime & paint.
I'm thinking over the years it's been patched & welded and to use based on use like a bush hog or finish mower would determine what spindles & blades I'd install.