You know, refitting ships is really no easy matter. It's not like there's a bunch of wiggle room built into the hulls.
If you tried to take a modern aircraft carrier and do the equivalent of swapping some Terran Turrets for flaks - say, replacing the Phalanx guns with Standard missile launchers - it'd be a nightmare. You'd need to make all that room for ammunition, reengineer the hull...just impossible.
Same with trying to slap some battleship turrets on a destroyer.
So all this 'swap the beams for Vasudan versions' is even more unlikely. We're talking about reworking the power network (who's to say they operate on the same 'wattage'?), the software, the targeting systems, the heat sinks...you might as well build a whole new ship.