You may want to email Ballard Rifle Co. in Cody, Wy. and see if they can assist with your question.
You might also want to get a copy of John Dutcher's book, Ballard, The Great American  Single Shot Rifle. It doesn't have detailed dimensions, but it does have some great close up views of the Ballard extractor.
The extractor on a #2 was never designed to extract a .22 RF cartridge. The Ballard #3's, which were designed to shoot a .22RF, used a completely different designed extractor system. The #3 extractor was a round rod that pushed straight back, rather then pivot on the lever screw. A #2 style extractor can be made to extract, but they generally need to be carefully loaded, so the rim of the small case doesn't get under the extractor. Not a good choice for little ones, who just shove them in and shoot! I'm sure you'll be supervising, but do you want to load each cartridge for them too? Good luck with your project! Hope this helps.

I have an old #3 barrel left over from my Ballard project that I will donate to the cause.  It is somewhat the worse for wear and has been relined at least once.  It does have an original front sight.  It has the hole bored for the .22 extractor ( and some other machine work to make it work) and may be useful for your project.  It present, it is just taking up room in my shop.  Send me a PM with your address and I will ship it to you.  My gunsmith converted a centerfire action to rimfire and had the devil's own time figuring out that extractor.  We used a new one from Ballard and had to make a lot of changes to make it work in the converted action.  I wouldn't rely on DeHaas too much.  Best of luck-it will be worth it in the end.