Although I haven't run the numbers and can't say for certain what pitch that would produce, it isn't what is shown on the threading table of metric threads for the 9" and 10" up through 10D. For the table (and other information), go to DOWNLOADS and download Part 7 of the original version of the MOLO.
Well, not really. You shouldn't have either multiplied or divided by 2 as the 9" and early 10" don't have a Tumbler and the Tumbler gear on the early 12" is a simple 32T, not a compound gear.
Also, you do not need to machine the teeth off of the 20T gear. Any place where one of the charts shows "20S" you just use a 20T gear as a spacer. It's teeth do not engage anything. If you happen to have an extra spacer, you can use it if you wish.