ref your message I dug up
"I also am using the Pertronics ignition in my 1960 golde top. I have the Mallory Unilite optical ignition in my 1959. I am running the the stock mustard top coil. I have never thought of widening the gap on the spark plugs. I would not think it would make that much difference in gas mileage. I might give it a try."
I installed a Pert on my 65 Mustang 289 4V and got great results BUT it shakes at stop lights -- when installing plugs on my 75 460 TBird with electronic igintion I found the spark gap required increasing because more fire is coming through, this raised the question as they are the same plug size and the gaps all seemed to change around 1972 when Ford went to electric igintions. I have not changed my 65 yet but have asked a lot of experts and they did to agree Pertronics should address this.