Travis,
I don't have that measurement but my concern is how are you going to secure the rod to the spring cap. I would be hesitant having something that could come apart inside the injection pump. Also keeping that rod dimension consistant may be a long term concern. If the rod dimension slipped just a little, it would easily throw off the cold running mixture and possibly the warm running mixture.
I would bet there are thousands of those WRD units in salvage yards you could get a good rod assembly from. Probably wouldn't hurt having some spare WRD parts and shims anyway.
