Actually the CEN Matrix BUGGY uses 26/9 gears in the diffs. The truggy uses 38/11. Its still rather high for a truggy (actually very close to what most buggies use, 43/13) but not as bad as what you originally thought.
When I converted my CEN truggy I found the same thing. I started off with a very low KV motor to compensate for the tall gearing and 46T center gear. Eventually, I actually switched to the Hot Bodies 43/10 truggy dif ring and pinion to lower the ratio and allow the use of a 46T spur gear without a super small motor pinion. The HB ring gear and pinion fit the CEN difs with a little careful shimming to get the mesh right.
EDIT: What are you planning to use for chassis braces? The stock over the top braces dont look like they will work with your center dif arangement.
Here is a link to my CEN Matrix TR thread in case you are interested.
http://www.rc-monster.com/forum/show...ight=matrix+tr