So, is this a mid-70s Cilo with 1st gen Dura-Ace? 531 frame & forks? As a member of the Cilo-owners club, I'd love to see pics. I have an early 70s Cilo that came with a mix of Campy and other continental parts. Cilo also sold a number of re-badged Vitus 979 frames in the mid- to late-80s, which were often built with Dura Ace 7400 groups, but I suspect you have an earlier one since you are looking to replace a 5-speed FW. I don't believe Dura Ace made freewheels with their 1st gen group. My Cilo came with a Sedis chain and Atom freewheel. Those come up on ebay with some regularity, but you're likely to pay a premium for NOS Regina or Sedis chains. The premium paid is for retrogrouches (like me) and is not directly related to performance. I'd recommend a Suntour or Sachs freewheel if you want vintage, and a new chain to go with it. Chains are not my expertise--I tend to stick with a few favorites--but I know several members swear by modern 8/9/10-speed IRD chains on 5-6-7 friction drivetrains.

I'd also recommend a side of bacon. You're missing out.