What year did they switch to overflow bottle radiators?

You don't need to change anything. Recovery systems burp/ expand back and forth as it heats and cools into the overflow bottle. You do need to make sure you have the proper cap as different radiators have different neck depths, and of course you need a recovery type cap. The only real difference, is the lack of ears to make it more difficult to open, and a gasket for a perfect seal on top of the cap.