I like "retooling" over "retrofitting" so I'll reply here.
First off, accept you're doing this backwards; we usually pick drivers, first, then build the box. The result is quite a few tradeoffs, the biggest is that we're going to replace most of the front panel of the speakers. This is unavoidable because you will use different drivers in different locations.
If you feel confident that you have the skill to end up with something that looks like she'll want it in the house, much less even let it in, the next step is to measure the width of the box, outside, and the volume of the box, inside.
- width of the speaker is an important design variable you'll want to match fairly well
- volume of the box will interact with the driver(s) selected to give you good bass
Then you can start looking at "proven designs" to see if there's one that's a good fit. "Proven designs" are the combination of drivers, crossover circuit, and box design that yield a high-performance speaker. If you find one that's close to your baffle width, and doesn't require a larger box, you'll have a candidate. Compare several candidates to see which is the best fit overall.
Now, keep in mind that it will almost be easier to build new boxes, but they won't be as pretty, and I'm betting that pretty matters.