$600 is probably reasonable, or even on the low side if the bike is in good shape and is all original.

Colnago Super models would also have had nuovo record components. Double check frame markings.

Does it have sewups or clincher tires. That may make a difference for general ridability, although there are much better tubular tires + sealants available than there were 30 years ago.

I'd keep the original shifters for now.