An Alpha III modified to use 24mm Estes D motors will probably be marginally stable, if not fully unstable, and require nose weight to fly safely.
Modifying the Alpha III to fit the Estes D's would require extensive cutting and jury-rigging tube junctions, etc etc., enough so that fairly early on in the process (about 15 seconds) the question should occur to you, "I am an idiot for putting this kind of effort into a rocket I am never going to see again."