After 5 months and 7,000 miles, I re-did part of the repair in my first post in this thread.
I apparently did not mix and apply the epoxy putty as throughly as I should have, and also used teflon tape, which was causing the material to crack and seep coolant and steam. (I was replacing about a quart or water per week.)
The epoxy putty was used around the copper bushing. The JB Weld surrounded and reinforced the "L" part of the radiator neck. (Not surprisingly, the JB Weld part of the repair is still holding up strong.)
This time around, I used only the putty, after
gently tapping the copper bushing more deeply and snugly into the radiator neck. This second repair was fast and easy, using materials left over from the first repair. So far, I have not lost any coolant. (The reservoir is still topped-off after a week.)
What I find curious is that now with the coolant system completely air-tight, my engine is running hotter than it did when it was leaky
I thought the opposite was supposed to happen.
Interestingly, on my last visit to my mechanic's, he had a nice collection of broken-neck radiators -- all of them with the new metal inserts! So no matter what, these things are destined to fail at some point, and I am glad I chose to spend $5.00 and about an hour to fix mine rather than $300.00 to replace it.