Engine shakes BADLY!!

Ok so I just finished fooling around with the car, and no matter what I did with the carb it still shakes a lot. So then I checked everywhere for vacuum leaks one again and nothing...... While messing around with my curb idle I noticed the car shakes so horrible at 1000-1100 rpm. And of course when the engine makes more vacuum. If I get more rpm then 1200 it smoothens out. I went for a little rip with my idle set a little higher (1000) and I seriously thought the car was gonna shake it's self apart. My fillings in my teeth were falling out! Once back on the gas smooth.
My buddie got ahold of scatt and they gave me a part # for a balancer/damper I should be using.
My engine builder said they used the same damper from my 340 which was internally balanced by them. Below I've posted a picture o what my current damper looks like. I found a part number but can't fine any info on it.
Part# 128668 current damper
The back looks like this picture