Agree it is a 1991. The dropouts made me think it was from the 80’s.
Others have chimed in, but is it index shifting now. I don’t recognize the shifters and I don’t see SIS and Shimano and Suntour don’t play together very well.
This would still be a tough decision. I can tell you how I have approached it with my wife. For over 30 years, I have tried to get her the best I could find, within reason, set it up to be as easy as possible, and more importantly, a bike she would like; starting with Shimano 600 SIS shifters and derailleurs in 1986 to replace friction shifters. Happy wife, happier bikeman.
You need to think out if you want non-ramped flat chainrings with your brifters. My wife used them with a double, but her current bike is a triple with ramps and shifts much easier. Also, I thought the ‘91 Cannomdale catalog list an ST600 (no racks) at 25lbs. If so that is one more thing.
John