I marked and cut one side, then used each cut piece as a pattern to cut the other side.
Some trivia for other builders: I needed 134 screws: all 1-1/2″, except for two in the outside rear corners that are 1-1/4″. I used flat-head Frearson bronze screws, with the heads slightly countersunk below the surface.
As soon as all the floorboards fit nicely and the screw holes were drilled, I removed them and set them aside to start work on finishing the interior.