Not a Model 66-3, but here is a photo of my Model 66-2 with 2.5 inch barrel. This was my first S&W handgun, and an absolute joy to shoot. I agree with the others about not scoping your Model 66. I tried to scope (actually, a red dot) a 4.0 inch barreled Model 625 - which is an N-frame, rather than a K-frame like the Model 66. They do make a scope mount that does not require drilling:
Revolvers
Frankly, the balance and weight were to much for me to even try shooting the piece. Enclosed, please see the photo of my scoped Model 686-3 with 6.0 inch long barrel. The Model 686 is an L-frame revolver (think beefed up K-frame), and I think the 6.0 inch barrel balances out the weight of the scope and mount very nicely (that's a 2.0x Leupold scope).
Regards,
Dave