You can probably find drivers that fit the cutouts, and you can certainly find pre-made crossovers that are close, and you'll get reasonably good sound.
However, you also have the option of replacing the front panel (baffle) and installing a modern, high-end speaker design. In effect, you can use the boxes to hold a top-grade, proven design. The only requirement is to find a design that wants a baffle width that's close to your enclosures, since baffle width is a major design parameter. Designs specify the drivers, their mounting geometry and the crossover circuit. Many also include one or more box size options as well. Some are free for non-commercial use, others are sold as kits (usually very reasonable).
Here's the master list (don't get lost in it):
http://techtalk.parts-express.com/sh...d.php?t=211558