The item listed is a genuine Vx part, when the Calibra and Cav were having oil cooler problems in the early days of the V6, GM produced a Kit which included the updated cooler, cooler plate, new nuts and O rings against part number 93176626. This part is listed in TIS in the relevant TSB.
This part number is NOT listed in EPC but can be ordered from Vx by the dealer (if they can be arsed to go onto the Vx parts ordering system) and costs MUCH less than the individual parts.
Contents of the kit are the same as the individual items.
Your original cooler will have been stainless to, the issue is that people instantly think that stainless does not corrode when in reality it does, particularly if there are any salts or impurities etc in the system (there will be), its good antifreeze service intervals that keep the cooler etc in good condition.
The copper look is from memory a coating which is applied to the steel to allow it to be resistive welded so no cause for concern.