Very nice.
Yes, the Atlas design where the speaker enclosure is integral in the motor cradle results in a very imperfect enclosure cavity with very little air volume It likely even isn't air tight. You basically got rid of the stock Atlas speaker enclosure and went with a more conventional speaker install.
Bill, I like to mention a small clarification to your video. Metallic lead is quite conductive. Most electrical solders contained lead, and lead-acid batteries in cars use lead as one of the electrodes. Moldable lead is made from some sort of putty or clay with lead powder mixed into it. The clay makes it non-conductive. Also, since moldable lead is not as dense as metallic lead, if someone wanted to go through the extra trouble of filling the speaker space with metallic lead, it would likely result in an extra gram or two over moldable lead.