I've run OS Turbo plugs in my Novarossi and RB engines without any problems or leaks. The only plugs that I will stay away from are the (Picco/Mega) plugs. They will leak and you cannot use OS in a Turbo Picco head. I tried.
I'm trying to remember what a OS 6 is. I do know off my head.. Novarossi 8 super cold, 7 standard cold, 6 mild to cold.
Just my 2 cents
Herolin <---Traded my Airtronics for an Ipad and Laptop...
Soon to be GHETTOPRINCIPAL..