Hi bozzez, can u pls help me to know what is the "factory' headshim inserts for a Nova plus 21-5T and a Nova 421bsx?.., i got my engines 2ndhand and i want to go back to the correct/proper headshim gaskets. and also is it alright regarding performance and lifetime of the engines if i use O'donnel turboplugs in my Nova's?....thanx thanx very much in advance!!!