No, you're not shoehorning a DN graser into a LAC.
The BC grasers are smaller and much less effective. Not surprising considering that a BC is something like 10 times smaller than a DN..the advanced LACs still have to use different components though.
The HH Mod ships are mounting less weapons overall than the actual ships, just to keep things somewhat sane and avoid SE4 screaming in pain and crashing.
Phoenix-D