Here is an amateur view: Assuming it is too late to consider a Compound DC motor for this application or to oversize the winch, so maybe do the quick and dirty fix of a spring loaded take up pulley, probably dampened to avoid surprises. This would give your AC rotor a chance to hit design rpm...
ScottI2R: Did you find the resolution of the scale? If it still matters, I have a Futaba CJ3024 with 2 SM305A and one SM205A and the CJ says it can show .002, .001 .0005, .0001, .00005 or .00002 selectable. I can look on the scales if you are interested. The Futaba came from an Elox 8-62...
