I'm actually not quite sure if there is enough room in there for it. Syncros require a wider shift hub and there just isn't enough room. You'd have to make the gears about 20% narrower and the lower gear on the idler is already weak as it is.
I mean we just released our Xtreme Duty 4.70:1 gear set not too long ago with 42% wider teeth trying to combat the gear set's primary weak link:
![](http://www.marlincrawler.com/sites/all/marlin/files/u1/470XD/470xd_c_teethn480.jpg)
I think the next problem is that the transfer case low speed gear + idler shaft has a combined inertia higher than a transmission gear pair, so you'd probably need a dual syncro setup (like a late model R-trans) in order to get any sort of shifting performance out of it.
BigMike