Yes that would be my understanding, 3rd law is the principal player and the force is measurable in convential terms ie. lbs. newtons, etc.
To me it would appear clear, a drifting space vehicle fires its rockets, its combuster/nozzle array is spring attached within a plenum housing.
The feed in fuel pipes are flexible so the combuster is free to wobble on its springs.
As the rocket powers, the nozzle/combuster assembly strains against the mounting springs and drags/pushes/pulls, how ever you have assembled this in your mind, but it transfers the thrust to the main body via the springs and hi ho Cisco we're off.
But I could be wrong, one does not disagree with a Professor lightly.
"Thrust' is not a pushing force, it merely denotes movement." to quote the Professor. So the search is for an example of such, the rocket in space has been put forward.
As I read through the great weight of text on this subject i become aware of drawings which I already knew of. These show magnitude arrows on the inner and outer surface of the combustor/nozzles, the inner being greater, proof positive perhaps from those that explain the theory. But what is the magnitude of this force? Calculus will take me there I guess but not my forte. I am also drawn to comments regading optimised pressure on the bell and it does not appear high, I wonder is this pressure a simple correlation such as wing loading or is there more at play here.