Once the sidies are completed butt the 8" factory edges up agaisnt each other. For the Stern you want to measure in 2" and for the Bow (Stem) 3". While they are still butted together measure down the length 48" . Use a square to mark the centerline.
Next cut out the out the stern and bow triangles. At this point I suggest marking the sides so that you end up with both sides matching when you install them.
Set them aside for now