The triple barrel design was really just an attempt to try something a little different. Seems everybody and their mother are making a standard 6 barrel "gatling" gun when doing a multi barreled weapon

I'll reserve judgement on the "top heavy" issue untill we've seen the prototype: To eliminate the turret clearing issue the entire turret was raised a bit on a small disc compared to the original concept, which is a bit unfortunate, but unavoidable. On the other hand the entire hull has also been widened a bit compared to the sketch and even more compared to the original Enforcer (which shares the same height). It is dificult to tell how much of an issue it is from this particular angle IMO, but I agree that the twin guns are quite massive, compared to the single gun variant.

Right now it sort of reminds me of some of those planned WW2 German Super Heavy Tanks that never got produced (Can't remember the names right now)
With the flat bit, do you mean the small armor plate that sits between the front treads (I assume it was a typo

) ?
(here's a bit of photoshop magic showing the Mk1 and 2 Enforcers side by side. The relative sizes should be fairly close, thought the look about the same width. In reality the new design should be something like 10-20% wider, but about the same length)