I will start off logically assuming your 66's have original finishes which would be brushed stainless. If you rub Flitz onto the finish of your 66's you will change their appearance assuming they are original finish. You can "touch up" the finish on a brushed finish stainless steel with Scotch Brite pads.
There are basically three types of finish for stainless steel:
1. Brushed. This is most likely the original finish on your model 66's. It's a semi-dull finish in which you can see fine linear polishing marks in the surface. This finish can be duplicated or touched up with Scotch Brite pads and a gentle hand. Scotch Brite pads come in different levels of coarseness.
Light Grey, called Ultra Fine Hand - (600-800) 800 grit.
Green, called Light Duty Hand Pad - (600) 600 grit
Maroon pad, called General Purpose Hand - (320-400)
Work in a small area with tiny (1" square) piece of pad and stroke in one direction only following the linear polishing direction from the factory. Avoid any surfaces but the brushed stainless surfaces. The green pad can be used for all applications varying the pressure dependent upon the degree of the scratch. Look at You Tube for examples of how to do it or further research the S&W Forum.
2. Polished. Bright and shiny enough it looks like a nickel finish gun. You can achieve this with a polishing compound like Flitz (there's others), soft rags, elbow grease, and a lot of time. Or you can use power tools (see post by TANKLVMC). I'm not much for taking power tools to S&W revolvers.
3. Bead blasted. A dull uniform appearance. Can be touched up, supposedly, with a deft hand, hammer, and sand paper. Or you can take it to someone with a bead blaster or invest in a bead blaster. I'm not for taking hammers to S&W revolvers.
Good luck,
John
Scoundrel and Ne'er-Do-Well in Training