Ruby mk2 spark plugs ?

[Bob Culver]

On the same theme I do not recall mention of long reach plugs until the 1960s. The huge majority of plugs were not. There must be some reason why not almost universal earlier. Perhaps the large number of s.v engines brought risk of valve contact with many so the type was generally avoided.
From daily observation with my Seven I reckon plug gap effectively alters the spark advance The very recessed plug would certainly alter combustion.