A blued M66 with "CSP" is probably a Connecticut State Police issue. The SCSW says, Connecticut State Police, Model 66 in Blued Stainless, 4" barrel; reported that 750-800 were made, marked "Conn State Police" (or possible CSP, we are uncertain which) with a 3-digit number on the frame below the cylinder. Also reported that some have been sold as surplus with the black coloring polished off the stainless steel. Target hammer, .265" Trigger. Red Ramp, White Outline rear sight. The issue dates aren't given. If your has the number "781", that says there were more than 750 made, and "CSP" answers the question that it wasn't stamped with "Conn State Police".
What is the SN of your gun, the mfg. date can be approximated from that, but a letter from SWHF would pinpoint the issue dates. The SN can be found on the butt of the frame, if the stocks are target stocks you'd need to remove them to see the SN, but also look inside the yoke cut, if it isn't a round butt frame, the SN will also be there. We'd love to see some pictures.