Yes, changing out a driver with a new replacement is a task most should be up to. Just pay attention to the wiring (taking a photo of the original may help) so you don't reverse phase.
As mentioned earlier, I'm not as familiar with DAL as Duntech models but I believe John not only tested individual drivers, he then tailored crossovers to match desired response for each speaker. I'm told Duntech keeps records of manufacturer so that a similar driver (spec-wise) can be supplied for replacement. I don't know if that practice was continued with DAL or not.
A few comments regarding set up if you do buy a pair. I believe use of spikes is room dependent and that relates to suspension VS solid floor, construction material, and floor coverings. Next, my Princess manual specified a 3 meter distance for listening to allow the five drivers to converge properly. A 10' equilateral triangle set up can work nicely. However, distance from sidewalls in important and should be a minimum of 3', more is better. Lastly I understand the DAL models may have been a bit easier to drive than similar Duntechs. My Princesses were rated at 90 dB but John suggested a minimum of 200 wpc "for musical enjoyment". ;^)
Good luck. I too believe all of Dunlavy's designs (Duntech and DAL) hold up very well and can offer great bargains in today's market.