Sam ,the ACN prefix was produced during 1983. Making the one you're looking at an early 66-2.
The 6" barreled K magnums are the least popular, and the slowest sellers.
You would be hard pressed to find a finer shooting gun, but the rage these days are shorter barrels.
I followed an early 6" mod 66 through a couple of shows. The guy had a holster, a box of 357 ammo, and original wood grips. The shooter grade gun finally sold for $325,00
Personally ,for the gun you describe I would'nt pay more than $450. to $500.
Hope this helps, Best of luck ,,,AllenFrame