Well, I have been waiting. And watching. When I first posted this, the clam was retracted halfway down the inside of the shell.
It stayed that way several days.
I did nothing but prepare to remove it.
Then I began turkey-baste-blasting Rod's and ArctiPods at it. Once a day.
Then every 2-3 days when normally feed arod's.
It gradually, gradually started to re-open. Wrinkled/pinched mantle all around.
By maybe two weeks ago parts of the mantle were past the shell. One corner (closest to front right of tank, even when turned clam around) was widely stretched/folded inward. Stayed this way for couple weeks.
Now, I'd say clam 90% opened, that one corner just barely folded. Couple spots slightly wrinkled/pinched.
Watch it die now....