Spark plug question
Thank you guys for the help always my car I bought not knowing nothing about has ngk fr4 plugs in it 360 1973 1979 heads they are 5/8 plugs can you just change plugs from 5/8 from 13/16 plugs in it now are fr4 supposed to be gr4 or anybody want to tell me what to use thanks again for help haven't had a small block since 74
