Thank you for your responses! Apparently I am not alone in this. Thought I would provide an update.
The right front accumulator was also giving me the same trouble. I ended up undoing the fitting that connected it into the bleeder, and once I got that little U shaped tube free, I got it threaded in to the accumulator just fine. So I returned to the left front accumulator.
I had broken a short brake line on the left rear caliper, and I used the new line that I had purchased to repair that to chase the threads in the accumulator. Went in just fine. Then I took a new rubber brake line that I had not yet installed and used it to chase the threads on the hard line. Also no issue. Then I used a razor blade to chase the thread on the hard line, and removed a small bit of mashed thread. It still won't go on - it threads a bit, has resistance, then pops loose.
Looking at the shop manual, the line goes to a T fitting somewhere (I lost track as the line went under the radiator, I'd love for someone to tell me where the T is) - how hard would it be to just replace that section of line? Since it is essentially 3/16" brake line, can I get away with using a cupro-nickel alloy line as a replacement, as they are easier to bend and flare? I'm not sure about using flexible stainless line, as I would still have to cut back the existing steel line and flare it properly for the repair to work.
As always, appreciate the help.
v/r,
Robert