Agreed, aerodynamics in race car design were pretty much a complete black science back then, and other stuff that are common tools today were unavailable to race teams and engineers back then, or at least just the biggest of companies could access them (Ford's computer calculated suspension geometry of the GT40 - so space age!).
I don't know what was the exact motivation of the Kenyon's roll cage modification was, but having himself dodged the bullet more than once, Mel maybe wasn't willing to accept all risks anymore, or at least beginning to think about how to reduce some of them. Though apparently they had to learn it just isn't as easy as adding a few pieces of steel tubing.
But then, that kind of experimenting, including the failures, has always been a huge part of the fascination of motor racing to me. Something, who just know 'modern' motorsports with key ready customer racing cars, which are bopped down to a few thousends of a second for oh so exciting racetainment just can't relate to...
Real men drive pink cars!