@DanssuperO I know this isn't the buy-sell forum. But please tell your friend that I'm interested for $150 each if it includes the truck block (which is, if I understand correctly, the same deal he gave you.) In fact, I would like two, and maybe more in the future...
I think the stock transfer gear probably has 25 teeth. The custom transfer gear ("pinion") must have have 10 teeth. So the new gear ratio would be 25/10 * old gear ratio. 25/10 * 8.33 = 20.83 or about 21:1, just as Daniel measured.
Thanks again for bringing this up on the Forum!