Hi Lee
With regards to gearing, you can't gear an astute to optimal 17.5 race gearing. The pitch of the spur pinion is 0.6m which is the same as top force. With some careful dremeling of the gear cover you can create enough space for a 26 tooth pinion, coupled with the 70 spur it should go quite quickly.
http://www.stormerhobbies.com/cgi-bi...=cs&pn=BCA3040
That's a good option too