My preference is a cork arbor. Dacron backing only became common after the magazines convinced us every fish was potential record breaker. Many old fly reels are spooled with no backing and lots of level line (perhaps a couple different lines!). Backing the spool with Dacron adds more weight than cork. For the wood workers in the crowd, balsa wood or paulownia could work too, if sealed against water.
This old post shows fitting a cork arbor on a fly reel. The same process works for spinning and casting reels. It might take more effort to make a spinning reel arbor, but nothing that can't be done with sand paper and patience.
My favorite old spin reel is the Garcia Mitchell 304. No matter I how I look at it, the spool and drag are a really terrible design. I once filled a 304 with 4# mono, only to have the spool pop apart a few days later. An arbor or Dacron backing would have saved the spool.
Tom