On internet a page also showed an interesting video about the history of the BX4TC in the 1986 rally championship. Some of it were never seen earlier. See: https://fr.motor1.com/news/301978/citroen-bx-4tc-groupeb-1986/ (Picture thanks to Olivier Delhez)
This month the Auto Week Classics magazine (released in the Netherlands) contains a review of the BX 4TC by test driving the black Hueliez build BX 4TC. If interested, the magazine is 2019 nr 1. https://www.magazine.nl/abonnement/autoweek-classics