Stunerable Joe I will take a shot at this.
First off having a limited supply of 427 motors caused CS to use 428 motor in the cars. We don't know( I wasnot there) is if Shelby told the people he went to 428 motor because they where easier to get. The 428 made more torque than the 427 at a lower rpm. Either way this car would fly.With the gas they had in those days, 12.5- 14.5 compression was doable and silly power was there. If you where crazy a little nitro meth don't hurt for a couple more ponys.Compression was 10.5 for 428 and 12.5 or higher for 427 SO.
Back to cammers, Foot box had to be modified. Getting the motor into the chassic, I think it was easier to lift and drop body on chassic after motor was in. I know you need 2 shoe horns and 5 pound of axle grease to get them into a cobra. The 6 foot timing chain, My feeling is this, lack of enough
oil to cool the chain while running. The fact of no auto adjuster to keep the slack out of it for more accurate timing of the camshafts. I know on setup the guys have 4 degrees advanced and 4 degrees retard on the two heads.
I also think that the 427 LR then MR then HR and where designed and built already. If it was not for the Nascar issue with the hemi killing Ford, or NHRA and IHRA prostock racing the cammer would never had made it off the table for building.
I think for a long race of 3+ hours I would think that there was a issue with oiling of the heads and rocker shafts in the cammer. Over the years the guys learned to add return pipes to get the
oil back to the crank case and also add better
oil supply to the rocker assemblies. I also think that the chain would stretch and cause failures. Direct oiling and good steel chains would fixsome of this problem. I believe the guys running cammers are running a different style of chain to better control wear and stretch.
Power and rpm range cammer gets the win. Pushrod motor valvetrain in those days had it's limits. OHC where only limited by the motor bottom end.
I read that it cost silly money to make the 1,000 motors and parts for the cammer. We where lucky that ford wanted to win at everything in those days.
Shelby idea of keeping it simple added to why the cammer was not in lemans. 1 carb not 2 carbs, less moving parts to loose or break. Less power but better fuel mileage. I think that there was the idea of running at a lower rpm over having to whine up a cammer to get the same power output. Less revs, same power, longer life on motor and less wear on drive train. Maintainance during the race would also come into play.Less time in the pits, more time on the track.
I think we had aluminum heads on both motors in those days, so weight would be a wash.
Cammer is a great motor. the design has changed but the basic idea is alive and living today with most motors. Found an article, even GM tryed to build a cammer motor.
If I had silly money, the parts are being made again it would be cool to install a 500 cube cammer in a cobra. The problems of rockerarms, oil returns, and oil supply are fixed. This is a streetable motor and one of the coolest to look at and hear running.
This is not 100% correct info but simple thinking and some info would lead to this guessing. have to remember this was 50+years ago. Same place but a WHOLE different time.
Rick L.