Greetings from Texas
I am building my first bike, a retro beach cruiser with a Skyhawk kit. My goal is not to have the most beautiful, unique, or fastest bike, but rather to build the smoothest and quietest (and of course reliable).
In lieu of using thin lead sheeting between the tubes and the P7 epoxy filler in order to dampen vibration thru the motor mounts (special thanks to Bikeguy Joe for his wide and deep knowledge of this subject), I just ordered 1 square foot of 'Sorbothane' Vibration Damping Sheet Stock (1/10 x 12" x12"). Supposedly in absorbs 94.7% of vibration. It is much more expensive than lead sheeting ($17 for my piece), but there will be a lot left over for future projects. Stay tuned to find out if it was cost-effective viz a viz lead.
I am also looking into lightweight vibration absorbing foam applied as an expanding liquid to fill the tubes and handlebars in lieu of using lead shot. Haven't found the best product so far, but the internet is vast, and I am in no hurry since I will have only one chance to get it "right".
Finally, in order to make my bike look "less motorized" from a distance, I am working on how to create a custom low-profile gas tank that sits under the top tube rather than on top like a motorcycle tank.
Thanks for reading this.