I am about to start the assembly of the dashboard, instrument cluster, etc. I remember GM cars from the 70's often squeaked and rattled from the dash are. Are there any preventative suggestions while assembling? I though about a thin rubber gasket between the dash carrier and dash at each screw hole.
Any suggestions are appreciated.

You could probably get some 1 inch wide Teflon tape and place it inside the joint of the two pieces going together. Place it so its out of sight when assembled.

I wouldn't even cut holes for the screws, etc. Just go right through the tape and fasten.

Another suggestion would be a closed-cell adhesive backed tape, 1/16 inch thick by 1 inch wide. Do the same method.

On my Vette I used self adhesive foam weatherstripping tape 1/4" thick. Works very well

I am considering using the fuzzy side of some self sticking velcro that I have available. Seems like that should hold up for years, and is pretty thin.
It's nice that other people have had similar ideas.