Re: dampening idea
Somebody posted about the problem of the foam getting into the bottom bracket on motoredbikes.com.
I have tried to use this foam for filling other purposes and found that it does not fill nearly as consistently as you'd think.
What I would suggest would be to use some urethane sheet in your motor mounts somehow. It is risky to try to use rubber for motor mounts, because the fuel/oil spilled on them may chemically attack and degrade the rubber. Urethane is far more resistant to this problem. Stick to the harder durometers--60-70 or more.
Sorbothane is a premium type of urethane designed to absorb vibrations. It dampens much better than any other urethane or rubber out there. In the USA, Sorbothane (as well as plain sheets of urethane) can be ordered from McMaster-Carr.