I have a bone stock 70 340 Duster. Just replaced ball joints, tie rods, etc. I drove it down the street and good gracious...this thing has the most sensitive steering I've ever experienced. My dad drove it and he agreed. It does have power steering. Any input,suggestions or advice ?

Sensitive PS is kind of a Mopar trait, especially in comparison to modern higher-effort setups.
Put as much positive caster in the wheel alignment as you can get - stock parts will limit that so you can't go too far.
I'll assume toe & camber are in proper range.
There have been a couple of tech articles in Mopar Action over the years about improving feel.
MA is no longer in print, but you might find the info online or at their website - if it's still up - or try contacting Rick Ehrenberg.
He's a member here and also sells on Ebay.

i have a [factory] saginaw pump on my charger, and i followed e-booger's advice on shimming the spool valve in the pump.
i added a couple more washers than he recommended in that article, and MAN, what a difference that made !
as my car is not original, and the next caretaker can "restore" it if he/she wants, i could have gone with the borg [?] box, but the shimmed spool valve was a super cheap and easy way to improve the "feel" of the over assisted factory box.
as the car just turned over 19k original miles a couple of weeks back, it still has the original box, pump, and hoses, but very early in my ownership, i changed the factory woodgrain steering wheel to a 13" grant wood wheel to [kind of] slow down the factory steering.
it still has that same grant wood wheel today.

Actually, a smaller wheel will speed up travel relative to input, but increase effort via less leverage.
Or, put another way:
A larger OD wheel will essentially slow down the steering and provide more leverage.