I wish I'd seen this sooner - it would've been a bonus to have helped someone on my very first post since joining! lol
Amazing how many things remain the same (design-wise) over the years. I'm in the midst of giving my newly-acquired '76 Sovereign
31' a freshening-up and just removed the headboard two days ago - with the exact same screws/covers. My '76 is in remarkable condition yet the board material (heavy cardboard? Particle board? thin-sliver-of-MDF?! lol) didn't look... shall I say "healthy" on the backside. I plan to take it to a furniture repair shop so they can make a new padded fabric front for the wood I'll supply them, once I settle on a colour scheme.
Glad it worked out for you - all the best on your project!