Tonight, Ratty got a chain. I had a spare brand new chain sitting on the shelf, courtesy Dennis Kirk. A 100 link 420 chain.
Exciting rear shot of chain installed and adjusted:
Front sprocket is a 17-tooth DRP unit I picked up from Beatrice Cycles many moons back. Stock front sprocket was 15-tooth on the 140cc motor, and 13 tooth on the stock Cub 50. Hopefully this and the bigger rear tire let's this bad boy run over 50mph.