If you have the hollow-core doors then just plan on cutting the bottom of the door to the height that you need. Use a straight edge and a razor blade to pre-score the luan plywood and cut with a fine blade skill saw. If you stay a hair away from the razor score then the luan won't chip up. The underside won't splinter b/c the blade is cutting "up".
Here is the trick: When you cut that much off a hollow core door, you cut the bottom wooden edge right off and you have cardboard stiffeners showing inside. I always use the piece of wood that was inside the cutoff piece to re-fill the now exposed hollow end of the door. You need to remove the luan plywood from the piece of wood with a table saw. Then knock off the little end pieces and the new insert is ready. To prep the inside of the end of the door, take a chisle and cut back any cardboard stiffeners and glue that will impede the wood piece from being pushed up into the hollow end. Dry fit it and then use carpenters glue and some masking tape and/or a couple brads to hold it together while the glue dries. Then use sandpaper on the bottom edges and corners.