Hey Dedhed -- I feel pretty certain this is a cassette. For one thing, there is simply no place to insert a tool to remove a freewheel. Then I found this post by a guy on Facebook who confirmed it. Kind of searching for a video of somebody using two chain whips to remove the sprocket that is acting as the lock ring, so if anybody is still interested in this saga and can point me in the right direction, I'd appreciate it.

Not sure if the Facebook link will work, but it's from Bill's Vintage Steel Bikes, a post from 2015. In his photos though I just realized he is showing a seven speed free hub, not a six speed. So maybe I am just wrong. Seems unlikely that I would have somehow stumbled on to a rare six speed cassette.