MSD & ignition plugs + plugs gap...

Spark plugs depend on engine and configuration.
The coldest stock plugs on a smallblock were RN9Y, only on 1960s 340s IIRC
But even with a 340, an RN12YC may be needed to minimize fouling of the tip in street use. Depends how its built.
As far as gapping, I'd keep it conservative for better reliability - around .045" Experiment from there if you want.