I don't necessarily find comfort in using Wilkinson as a guide. He has his own purposes in mind.
If you are asking me about the cap on my Motorcraft, the male cap is not for a Ford. The original application of the cap is for an International Harvester 350 v-8.
Without measuring anything, I would say that the male cap is made from a modified mold for the female terminals cap.
The centerlines of the individual terminals are the same as is the external outside dimensions of the female cap.
The difference is that the spark plug wire boots for the male terminals are smaller in diameter then the female boots are and that is where the clearance comes from.
I also have 1-1/2" thick foam sheets covered with mill polished stainless steel sheetmetal panels on the firewall so that closes down some of the clearance space.
Again without measuring, it must be that the "Ford" distributor is not as tall as the aftermarket versions? That is the only specification that would effect this issue substantially enough to cause clearance issues to the cap and the spark plug wire boots?
I'm thinking that the features of the Progression distributor are a great idea but also that for a Pantera, the internal device should be built into a Ford distributor?
In a previous post, Bosswrench mentioned that the Pantera drivetrain can be moved back up to about 1-1/2" to gain more firewall clearance without issue to the u-joints on the transmission.