Sorry, this took some time!
You can find the story in some sites,but we must remember it was year 1986, what we are talking about here. Not much rally sites at that time
I asked this from Henri`s brother Harri Toivonen (fine rally/race driver he too, well ok their father Pauli win the Monte Carlo!!).
So,here is: Henri drove some tarmac tests in Estoril (yes the GP track) with Lancia and results were as it is here mentioned! He had "passanger" next to him,who had some "health problems" after rounds! The driving lines were a little diffent than F1 cars had, because of slide!
F1: Henri tested Rotmans March F1 and was faster than the real driver, not much but anyway...
I hope this helps??..