Yup, then took it off and put a fixed cog on
As long as you get the chain line and chain length right then you shouldn't have any problems.
Standard english hub thread is 1.37" X 24 TPI and the same is true for multiple freewheels and single speed sprockets.
I've used a set of miche hubs from the mid 80's and a brand new dicta single speed freewheel with no problems whatsoever.
Keep the 5 speed block and chain, line up the nearest sprocket at the rear and change the front chainring to get the gear in inches that you need..... just a thought