Why not just use a tape measure? Can't you just figure out bolt hole pattern and then just lay it out on the new piece? Like in the photo, it shows a 4 hole square bolt hole pattern. So you would just measure the distance of center of hole to center of hole (usually easier to measure front side of hole to front side of hole or back side to backside). Doing this to each set of holes (side to side, top to bottom and diagonally). Then measure the whole area to see what size of plate will work. Then figure out where in the area the bolt hole pattern is and all that is left is laying out the measurements onto your plate. Then you center punch the spots you want to drill and then drill.
Does this make sense?
Edit: For non blind thru holes you can always use transfer punches...