important note Sorry for the bad news but The bike is not "still driveable". If there is a sizeable chunk of metal roaming around in there sooner or later it is going to jam the gears and lock your back wheel.
and you won't like that when it happens
Is that $200 craig list engine we were discussing last week still around? It might be quicker to buy it and swap, you can then fix yours at your leisure and sell one or the other later to recover the cost.
https://www.ninjette.org/forums/showthread.php?t=186159
Okay it's in Atlanta
but check ebay, breakers etc'