Yeah, sure enough the K is flexing; the box is perfectly rigid. My Dad has an 80 Diplomat that we did this install on too and it doesn't flex at all even though his Dip uses the same K as my 87. There is a difference though...



Here is a shot of the mount from underneath on my car. My father's car has no space in between the box mount and the K like mine does. Unfortunately Firm Feel doesn't have a support kit for M body cars; I guess I'm going to have to weld in some kind of a patch to shore this section up.

Thanks for the input guys.