On track test are really not valid because there are too many variables.
Driver being of the largest variables, chassis setup being another huge one.

I have said this numerous times that the data is only as good as the person reading it. There was another post a while back of a person offering free time on a 4 post shaker rig for testing, nobody took it. Namely because number one, you have to come up with a test that means something, and two you have to be to interpret the data you got from said test.

BTW the K does a lot more than hold the frame rails straight. Again, some things you can't measure statically. It has to support the lower control arms as pointed out, and also support the engine as well as counteract the torque.

Just because the aftermarket K frame doesn't look as big as the factory, doesn't mean it's as strong, or stronger...

A Torsional Rigidity test can be done with the K installed or not, the better the rails are without the K installed, the better it will be with it installed.

My suggestion would be to twist the K members out of the car.

CR