Here is the bore reducer you will need:
http://www.rc-monster.com/proddetail...rod=RCMreducer
The CRT.5 does use mod1 gears. Using this calculator (made by BrianG):
http://www.scriptasylum.com/rc_speed/_top_speed.html On a 14 tooth pinion on 3s lipo, you will be right under 40mph. You can play with the values though to see what set up/speed you like.