It is a simple lever actuated mechanism. In order to lessen the stroke, linkages and pivot points would be effected.
In other words, in order to have the bolt move a certain distance, the linkage would have to be changed so that less angular movement of the lever would be required. That would require more force be used in working the mechanism. There is just so much room inside the receiver for linkages, so a major redesign would be required. You would most probably lose the smooth actuation the Henry is famous for by lessening the mechanical advantage inherent to the design.
I am unfamiliar with the Winchester mechanism, but I would be curious as to how the folks lessen angular lever movement. There would have to be some change in the internal lever arm pivot points.
It would be less expensive to purchase a rifle having a short stroke mechanism rather than trying to alter a Henry.