I just got out my bathroom scales and did some measurements:
Unladen weight: Rear 100 / Front 78 Lb Ratio 56/44 (not too bad)
Total weight is 178 lb. Reducing battery pack with Lithium will not dramatically reduce LADEN weight.
Rider sitting in forward position: Rear 210 / Front 125 Ratio 62/38 (hmmm...)
Rider sitting at rear of seat: Rear 235 / Front 100 Ratio 70/ 30 (this is why it is squirrely on loose surfaces!)
On the bright side, if you lean back while riding, you may be able to do wheelies! ;-) Seriously, I'm not sure how the typical motorcycle is balanced, so I don't know how far off ideal your moped is. Anybody here know?