The 249 is basically a "brick"...so it's definitely more generic to work with re. space/layout. I suppose any mechbox can be modded to be activated by a switch (so no trigger worries) but with the 249 box you're half way there. There is no semi on a 249...so it's full auto only and the piston is basically going to stop wherever it will just after you release the trigger. Technically you could just remove the gear stop and it would "unwind" as the piston is pushed forward.
Also...the hopup is basically a cylinder with a hole in the side for feeding...whereas many other hopups are bottom fed (because they're meant to be fed from a traditional mag).
From what you've described in that pic...you might actually be better off using the internals from a 249 and the outer from something else like a big water gun or nerf gun.