A904 Lockup Converter Won't Unlock

I just picked up a 69 Dart with a 340. Purple cam of some sort, headers, intake, etc. It is running an A904 with lockup converter that appears to be locked all the time. I've seen where you can use a ball bearing in the lockup valve to disable the lockup which I may do. Is there anything else I should look at first?

Thanks,
Jim

Usually a converter that won’t unlock is caused by the hydraulic applied ring that presses the clutch disc inside is jammed.
Never seen one that was caused by an unwanted hydraulic application.