A body K member

The resistance to going with the 1967 unit is entirely based on the idler arm mount.
They are not as rigid but for easy cruising, it would be fine.
The idler mount would probably only be a problem in a car with wide tires set up for cornering or on rough roads. The resistance to deflection is greater with the 1968 and later models.
I aim for what works best in a handling application.