Apparantly the roll bar is really good for stiffening up the chassis. Personally I did my own chassis modification (as I like to tinker!) But for a lot of people it is just the ticket.
For the roll bar:

http://www.neweramodels.com/cgi-bin/...rs&part_id=372

For a 125cc fuel tank (the MT2 upper chassis brace will have to be modified):

http://www2.towerhobbies.com/cgi-bin...24&FVPROFIL=++

For a 100cc fuel tank (will still need slight modification, but is not as big):

http://www2.towerhobbies.com/cgi-bin...e2&FVPROFIL=++

For the 4wd conversion kit:

http://www.rcmodels.com/rc-cen-ffs026.html

Do check out the posts here, there is a lot of useful information.....Cheers....