Re: RCGF, the beam mount version is pretty strong, stand off version not as much.
Dubro soft mount has rubber grommets between the motor mount and the firewall
http://www3.towerhobbies.com/cgi-bin...?&I=LXD633&P=7
A lot of guys prefer something like this one:
http://www3.towerhobbies.com/cgi-bin...&I=LXATG7&P=ML
Total weight is 750gr? With muffler and ignition? - Not very likely. If they don't specify what the spec. includes, safest bet would be it's engine only?