I wanted to try my Feadog/Walton hybrid tweaking on some Acorn whistles becasue I suspected that the barrel hole size and placement were the same as the Feadog. I found a great price for the Acorns ($4.95) on http://www.marsmusic.com so I got a few to try putting the Little Black fipple on them. I was right that the hole size and placement were the same as the Feadog but what I did not anticipate was that the painted barrels were too thick for the fipple. I had to use sand paper to get the paint off the end of the barrel to fit the fipple on. The brass Acorn was no problem.
So if you want to try my tweaking experiment on either Acorn or Feadog painted whistle it is more trouble than the brass whistles (but the final sound was just as good).
Joe