I would check the toe-in like the old mopar manual says, ride height, then lifted an inch and then pull the car down an inch. If the toe is going too far positive on deacceleration when the front end sinks, it can cause a shimmy. I race a 64 doge NSS car as well, and mine did it years ago. I found that setting the front end ride height to factory stock specs, and adding a little toe-in fixed my problem. Mine started doing the shake when I tried to lower the front of the car. I also installed a set of these type strut bars, really helped make the car drive nice. When the suspension goes through it's movement, any deflection of the strut rod bushings, really affects the caster, on the car. and these will let you dial in a little more positive caster if needed. And as mentioned, make sure all the suspension is tight, no looseness anywhere.