Chains for a vintage bike are a problem. The big problem is that all derailleur chains made today are optimized for indexed shifting systems. They are far more laterally flexible than we’re the vintage chains. Older non indexed rear derailleurs often had a design where idler pulley was positioned some distance from the cogs. Indexed systems are the opposite. This was great for quick and easy wheel removal, but not so great for shifting with a flexible chain. The old Regina chains were very stiff and even the old Sedisport was stiff by today’s standards. I use SRAM 8 speed chains sometimes, but find that the Wippermann Connex chains are a little stiffer and work better. For the most part, I have gravitated away from 7 speed freewheels to 6 speed as they are far easier to shift with a modern chains. I find that it is also helpful to exaggerate the “ overshift and back off “ method of shifting as well