Thanks, the author knows that too as he outlines all of the different models.... but he made a specific comment that the Vauxhall 2L 20XE 'should' have one tank of leaded every 4 tanks of normal unleaded 'if' using carbs...the twin DCOE's.
I am guessing he is saying the top end, valve train, requires a bit more lube (lead) due to the heavier fuel washing effect of the carbs compared to the other fuel injected mode. Just a guess here.