Take a look here [link=http://www.rcuniverse.com/forum/m_5303671/anchors_5303671/mpage_1/key_/anchor/tm.htm#5303671]CX 1½[/link]

I converted a CX to a "CX 1½" by adding a 2.4ghz 4-in-1 from a CX2. The chassis (and servos as ndoren points out) are indeed different.