I've decided to go with either a Suntour or Shimano 5 speed cluster, NOS. I've sourced several different models and tooth counts and they'll fasten to my English threaded hub with no problems from all that I've read.

NOS Mailards are out there, but rather expensive and apparently not as good a quality as the higher end Japan model offerings.

Heading out to a LBS tomorrow, who has what I need in stock.