After 46 years of my Norton and using copper head gaskets I only re-torque at the first 500 miles and never had a problem with blow outs
I have build a few Norton motors over the years and always use copper head gaskets, the composite gaskets need to be re-torqued more. I have only used a composite gasket once and it blew out, never had that problem with copper, I just did what the bible (manual) said to do., has always worked for me.
But of course everyone has a different opinion of re-torqueing heads.
Ashley