I haven't read that whole thread you referenced, but....
I had those exact slappers on my 57 Chevy (370horse 350/ Muncie). They clearly aren't installed correctly on the b-body. Those need to be slid forward or backward till the snubber is directly under the front spring eye, and nowhere else!
Then, adjust the height of the snubber till they work the way you want. Simple as that.
