I would like to know how much horse power will be gained by removing the power steering on my duster.

Not enough to notice while you drive. If you were comparing on a dyno - you might see a little difference.

Not enough difference to have to horse around manual steering. Or pay for another steering gear box and steering shaft.

The difference in HP would be while you are cranking the wheel agressively. Straight line very little loss.

Most of us that have done the swap from power to manual steering did it for the weight off of the nose of the car, I seem to remember 70 lbs. weight loss, maybe a little less, maybe a little more the pump, the two hoses, the fluid and iron power steering box adds up
You will need to extend or replace your steering shaft in the steering column and get the proper arm for the manual steering box, my luck has been the one from the power steering box won't fit the manual steering box from a different car
Other guys on here that found the manual box out of the same year, brand and model car they where working on had no problems with correct arm on the manual box

Weight difference is supposedly about 35-40 lbs. As far as horsepower loss, I've heard with the wheels straight that it's almost nothing. But then there is this: http://www.hotrod.com/articles/mopar-engines-power-vs-luxury/

1 maybe 2.... go for it . Totally worth all the effort

X3 on the weight loss bennie especially on the front end (it all adds up).

On a street style performance car the alternator belt is worth about a tenth to a tenth and half second just taking the belt off. I would guess the Manual steering would be the same PLUS the weight loss. If that kinda thing is worth your effort and expense go for it. For street driving and the ability to park your car keeping them is a good call. To each his own.
TOdd

One less potential leak. Header clearance.
Steers about like a 1952 John Deere when done.
Win/win, kinda...