If the L4 is any indication of the effectiveness of the Copias when it's in regulation, you should get an even performance from the A2 as well with the stock bulb (MA02). As the A2's bulb is rated at 6V, the Copias shouldn't flash it (the MN03 tolerates a Copia quite well, even though it's dim)...
I don't have much experience at all with machining, so I'd be the wrong guy to talk to about machining the ID of the A2 to accept a Copia. Although I would say there shouldn't be much to machine out, since if I were to really force it, I could get a 168B in, but it'll scrape the sides out. For reference, a 1/5A NiMH can still drop in, even though it's ever so slightly wider than a typical CR123 (probably by its own shrinkwrapping)...
Who knows, maybe even chiseling/sanding the insides enough could allow a Copia to fall in... I'd say, for testing purposes, you can just wire in a Copia or an external power supply from outside...