If you want a drop-in motor that requires no mods, check out the OS .18 cv-rx with the 11j rotary carb. Here is a link to it on Tower Hobbies:

http://www2.towerhobbies.com/cgi-bin...&I=LXGGP7&P=ML

Right now Tower has a $15 off coupon on a $125 purchase. So pad your order and get the discount, it's worth it.