Thank you, Frank, Marco and guyORS (who sent me a PM) for your hints. I have identified three possible "suspects" in terms of events, i.e. on 22/05/1977, 03/07/1977 and 31/07/1977.
I checked in AutoVisie to start with: Nothing in N° 12 (issue dated 04/06/1977) for the race on 22/05/1977, a good report in N° 15 (dated 16/07/1977) on the race of 03/07/1977 but not the slightest hint to the fact that there might have been Gr.6 cars (nice sunny wheather, tough - just like in my pics* ...). Not sure of the 31/07/1977 date as I did not manage yet to put my hand on an appropriate copy of AutoVisie.
One of the races (can't remember which one off the top of my head) counted for the French "Coupe de l'Avenir". I have the report in Echappement N° 106 (August 1977) but again no hint to a "real Gr.6 race" (apologies to all Coupe de l'Avenir fans for my wording). Same for auto hebdo (N° 70, 71, 74 and 76 in my files) ...
My "preferred suspect" remains the event on 03/07/1977, though. This snippet is from Autosprint where they say Gr.6 cars, as well:
At the same time, this ad from ONS Nachrichten does not mention Gr.6 at all:
* = all other pics just show the LBS team with both cars (LBS 3 and LBS 5) in the paddock; no other competitor left, right or center to allow additional identification
Edited by r.atlos, 21 December 2010 - 23:11.