RC;
My compliments on a good documentation...the bra analogy was unique and colorfully descriptive...I like it!
Looking back on the work, do you think it might have been possible to install HRs without "undressing" the seatback to get access to the innerds and frame? ...by feeling around and locating mounting tubes, cutting holes for access, and doing the rest of work externally? This is the way the retrofit instructions presented it (Fig. 3), and it would sure make for a lot less work! I'd be interested in your experience...I'll certainly link this thread in my article:
http://www.sw-em.com/headrest_upgrading_notes.htm
Cheers from Connecticut!