In theory your set-up should work except for very hot days.
I wonder now if your radiator is partly plugged.
This may not have shown up with your 216 but with a tight new 235 which generates more heat it has become a problem.
A few more miles may stop the problem.
It would have been much easier to install my adapter with the engine out but it can be done in the truck.
Yes without the radiator.
