A little back to your first question.
Owning both a Coupe (66) and a 2+2 (65 K) - and having had both extensively apart over the years I don't think you can use OVER RIDES in a Coupe and still retain the back seat area unchanged.
The 2+2 rear seat area is narrower than a Coupe - look at some pictures and you will see what I mean. The fiberglass panels on the 2+2 come in toward the center of the vehicle a lot further - providing some space for the bar to come in and attach without hitting the interior parts - this space doesn't exist on the Coupe.
On the Coupe - the inner panels hug the inner rear window area and the inner wheel well - AND the seat expands outward towards the doors. You can compare a Coupe and Fastback rear seat width to see the difference.
I think you could move the over rides as far outboard as possible and still not clear either the seat or the inner interior panel on the Coupe.
However, I think if you did move them out board as much as possible - you could modify the seat and rear panels to clear the bars - the inner part of the side panels on the Coupe is metal - so you can easily modify them "out" to clear the bars, then cut down the back seat to match the new inner panels. Of course both the panels and seat will need custom upholstery modifications to appear stock.
You could make a CV joint boot work if you welded a lip around the opening for a clamp or screws - picture a dryer vent and you get the idea.
I hope this helps.