Came across an "original" 1970 Duster 340 4 speed with a pistol grip shifter. Did someone add this shifter or were these factory original shifters in the Dusters? Another question.....Are these cars very desirable? Thanks for your input.

Sounds like someone installed the top part(shifter handle) of a E or B body shifter in that car, no pistol grip OEM shifters in A bodies in 1970 or later I believe
As far as who and how many people likes them it depends
I like them a lot, but I've always been speed needy
What condition is it in?

The car is very solid and 95%+ original condition. Just a little rust started ahead of the rear wheel wells.

No factory pistol grips in A-bodies, as far as I know, which kinda seems odd.
Shifter swap may indicate other changes from original, which may or may not be a factor for you.
Heck yeah, 340 Dusters are desirable, especially with 4-speeds.
Many feel that '71 is the best year, but '70s have a fan base for sure.
Check the spare tire well & rear body panel below the tail lamps.
Post some photos if you can.

NO pistol Grips for the A bodies, That's a B/E body thing only, although there's nothing wrong with adding one to any vehicle

The 71 to 74 bench seat pistol grip shifter handle works nicely in an A body.

I agree. Works well.