Engine shakes BADLY!!

Hey guys sorry I've been MIA lately.
Got some updates.
First of all that video posted is not my car hahaha. The link I clicked shows a yellow duster. Weird.

Anyways I spoke with my engine builder and the balancer is a neutral one. And he doesn't feel that's the issue.
I replaced the engine mounts with no change.
Today I put an old carter carb on and no change.
I also changed the coil to a msd blaster SS
One thing I noticed when all heated up is how the engine shakes. It's will be smooth for 2-3 seconds then rough for a second or 2. Then back to smooth then rough again.
Then when I crack the throttle open the slightest little bit it shakes like a paint shaker until I add more throttle or let off completely.