Spark plug recemondation

anything from a rc9yc to a rc12yc champion depending on your engine and fuel .
I would start with a 9yc and go hotter if need be .
Yea basically. Stock would have been RN9YC. R for resistor, N is - Off the top of my head - the 13/16" wrench hex, 9 is heat range (Champion's). Last C is copper, whatever.
But, you've got aluminum heads so its not really stock. So the wrench hex is whatever fits - you may need to use the C which is smaller hex. JJJ may have posted C for that reason. Edelbrock will know if its not obvious when you look.
As jjj posted, heat range - start coldest and see if you may want hotter to reduce fouling. Advice is usually to run as cold as it likes it.

Which brand ? Pick your poison. :lol. Heat ranges can be cross referenced.