We cut down a spark plug socket so we could get it on those 2 plugs and as suggested used an open end spanner to remove/install. Worked great. Used a grinder with a cut-off disc.
In North America rear signal lenses can be either red or amber. In most the rest of the world amber is required. Most vehicles made here in North America still have red rear signal lenses and in 1973 your Duster would have had both rear signal lenses with red. Many imports have amber. I would...
Bought the one from Canadian Tire about 7 years ago. Used it maybe 6 times and no problem. Works fine. It usually goes on sale a few times a year so if you can wait you can save a few bucks.