Turned out much easier than I had anticipated. I don't have two chain whips.. and found the S Brown pic on the Harris site difficult to arrange (using a scrap chain to hold a cog.. that held in a vice). So.. I just attached the free wheel to my bench.. using drywall screws with the portable drill. Taking care NOT to add too much downward tension when tightening them to avoid any potential bending etc. Two them came loose fine.. one was very stubborn which got a dose of Liquid Wrench. This last stubborn FW I used washers to shim the spacing between the bench and the cogs.. tightening them down then meant no possible bending. Cog to screw contact was very minimal.. to avoid any cog damage.
One chain whip.. the portable drill.. now I have that 28T on the end of the set.