I found the cause of my problems!
A beginner's or senile person's mistake and since I'm not a beginner....it means I'm becoming senile! 
I checked the firing order on the distributor head several times, I checked several times that the wires were correctly connected to the correct spark plugs BUT, I trusted my memory for the numbering of the cylinders and I was so sure of myself that I never checked even though it was very easy since the numbers are in 1/2'' digits on my intake manifold.
And I numbered:
4
5
3
6
2
7
1
8
instead of
4
8
3
7
2
6
1
5
And so the spark instead of occurring on cylinder 7 occurred on cylinder 6 which had the intake valve open and the same between cylinders 5 and 8 with the intake of cylinder 8 open.
What is surprising is that the cylinders on the driver's side cylinder bank still worked, certainly very poorly, but it was indeed burnt gases coming out of the exhaust.
I'm now impatiently waiting for my car to come back from the body shop to put everything back in order and check that it starts like clockwork and that there is no more backfire.
I still have little consolation, it allowed me to learn a little more about modern electronic ignitions and the precautions to take when wiring.