I don't believe the cutouts on the cassette cog would present a problem when they could be modified for freewheel body use. There are enough splines on the Shimano/Sunrace type body to make up for any inexact spots.
Looks as if ebay has what I need to get started on this project.
RMT Pneumatic Knuckle Press. It's local pick up only in CA. Can anyone facilitate?