1973 Dart 318 core plug replacement questions

It sounds tough if you never did one. Use a socket about the same size and either paint or rtv. If one is leaking then the rest are close Togo. I like to pop them all out. Flush the block with a hose and relieve the 40+ years of debris out. Let it dry and lightly sand the flat surface so the new plugs don’t fetch up on any thing.

Also spend the extra and go brass. You will end up with more plugs left over if you buy a kit but typically a kit is cheaper than the individual block plugs.
Good luck!
Syleng1