As has been mentioned by a couple of others above, this postdates the Raleigh takeover and Armstrong became just another victim of the badge-engineering that the British transport sector in general was so fond of from the late 1950's onwards; especially so in the motoring and motorcycle industries.
I personally don't think that quality became lower in the bicycle industry on the subsidary marques necessarily, its merely a case of different badges and paint schemes, that's all.
I think that the quality wasn't really there anyway at that moment in time, especially in the everyday bike market.
This may sound a little negative, but I think it reflects the general malaise afflicting moribund British industries.
Cable ends are different to the regular trigger type shifters.
You shouldn't have too much trouble getting a cable to fit, they're available below:
STURMEY ARCHER INVENTED THE TWIST GRIP IN THE 60\'s AND DURING THE 70\'s and the 80\'s IT WAS USED EXTENSIVELY 
www.bankruptbikeparts.co.uk
...sometimes you have to reposition the little gear wheel to get a good position.
Rear nuts are indicator cables are also readily available.
It wouldn't take much to make it into a very smart, useable machine. I imagine it could be popular over there.