Just a shot in the dark...about 100yrs ago I had a 67 Barracuda w/440... anyway one nite I went to a friends house and when I tried to leave no start /spark... every thing looked good just no spark. then I found one of the wires from the MSD-6C had gotten trapped under the Valve cover. Once I found and resolved the issue (plus learned another lesson about MSD's) it started right up...just a thought