Hi,
For ballast weight take a look here:
http://p-dubracing.co.uk/page5.php
The Ghea 2060 front bulkhead and the Ghea 2061 rear bulkhead, both of these are 30g each. (Also, Ghea 2057 / 2058, front brace.)
You can also add weight under the battery and under the servo, Rube Bits make a range of weights for under the servo & battery.
Details are here:
http://www.rudebits.co.uk/
The under servo weight is good for high traction conditions.
MiCk B. :-)