I just measured the OD of the 2 speed adapter that is sold in the rc-monster store. they 1st speed OD is 11.91mm and the 2nd speed OD is 15.82
If you are looking for a specific set of gears, Mike has a whole range of them made to fit the 2 peed adapter. I think the 1st gear statrs at 15T and goes up and 2nd speed starts at 20T and goes up but I'm not positive about those. ANyway he has a whole range. shoot Mike an email and he should be abe to get you waht you need.
I am using his 2 speed adapter on my DM1 conversion and am using 16/21
Get this:
http://www.rc-monster.com/proddetail...rcm2spdadapter
and this in the correct tooth count
http://www.rc-monster.com/proddetail...cm2spdgears1st
and this in the correct tooth count
http://www.rc-monster.com/proddetail...d=rcm2speed2nd
Its not clear in your first post if you are planning to run it nitro or electric, but if you want to run it nitro just get a Losi LST clutch bell, it should work with any stnadard 1/8 clutch. Then you could use these 1st and 2nd speed gears on it.
EDIT: Just to be clear here is a picture with dimensions of what I measured.