Generally, a bad idea. To be safe you would need to get a properly made fork with a mount that can handle the extra stress of the disc brake. No matter how much you add bracing to your current fork there are still twisting forces that can overcome just a fin brazed on. The twisting also contributes to your quick release not holding especially when a rack stay is clamped between the quick release nut and fork ends and as Andrew mentioned above, your fork ends are facing the wrong direction for discs. I like to experiment with lots of things too but a crash like yours would have put an end to that experiment for me. Be safe.
Last edited by Crankycrank; 03-28-24 at 07:15 AM.