How would you bend this frame back?

Kern Dog offered a spare frame bow he has. That is starting to look like the way to go
That would be the way to go. A good top shop MAY be able to replace it without removing the top. (Key word is MAY)
And I thought that when I bought this car I was going to wax it, lube the hinges and drive it into the sunset. HA
50 plus years, convertible, the Pacific North West - where you don't get a tan in summer you get a rust! Poor rust protection from the OEM, etc, etc, etc.

It is truly amazing that any of our cars are still on the road!