440 head noise. Perpetual problems. Problem solved

There is no heat riser on this one. It's been removed

All of it or just the outside parts? :D
Is the rod still there that goes through it?

Just trying to think of everything before you have to pull the trans and get a good look at the flex plate.
Have you run it with the converter unbolted from the flex plate yet?
(just long enough to eliminate that)
The plate won't usually make the noise if it's unbolted.