I took a closer look at the tailwheel fork I just replaced. It’s cracked through on the left side, inboard of where I welded it back together. The reinforcement that I welded on is the only thing holding that side together.
I’ve figured out the final solution I think, with some help from others:
This is Peter Anson’s 6” tailwheel. I’ll get a final weight when I swap it but I’m pretty sure it weighs almost exactly the same as my current 4” tailwheel assembly.