A point an old racer showed me, do not run the plug wires parallel. They can induce misfire under certain conditions by induction.

that was about 50 yrs ago and it was on a ford 292 or 312 cu.in. and it would do that because ford had 2 cylinders that was side by side in the cap and side by side in the head. if you ran them parallel to each other they would cross fire or jump fire some times. hey, dave or denny or one of you ford guys, get me stright on one of fords better ideas.