Yes I have checked for drive shaft yoke slop as it sets in the tranny. Non there. Compared to my 71 Cuda and it's pretty much the same.

Bell housing has not been dialed in. I wonder though that if that were the cause wouldn't I have other issues going on?

Replaced tranny front bearing.

Checking drive train alignment left to right would be something to pursue. I haven't checked that. U joints are good.

Mopar Performance super stock springs.

Yes gradual clutch engagement will still shake. If you just get it rolling you can boil the tires after that but hang onto your hats if you try this from a standing start.