Bing shows photos of the base on a Henry rifle, with the base overhang to the front of the action. Generally speaking, putting the multiple holes to the front allows mounting on different length actions.
The mount is made for Marlins, does work on some Henrys. Lay the base on top of the action, and see which holes line up with the mounting holes in the action. You want the base overhang at the front, not the rear of the action.