I just wanted to reduce how it looked like it needed to waddle:
(Just so you know, the lascannons are attached with magnets.)
Cut out middle groin-guard, smooth-out the side pieces at the back, glue to tops of legs.
On hindsight, I would probably cut off the first "knuckle" of the side and rear "toes" or off completely to look more in line with the "Contemptor" dreadnaughts.
I do like the "linebacker" look of these guys, I think there is a way to make it a bit more cool looking:
Cut the missile side bays out completely, clean it up so the arms pull in closer and maybe a bit down (will have to check how much plasticard to fix..
Then angle the shoulder guards down on a 30 degree tilt.
I would shave most of the rounded and raised areas on the back of the gauntlets till they are flat (still just above the level of the hands).
Then glue the guns / missiles on the back of the arms, green-stuff any nasty transitions and plasticard if the pod sides did not survive being cut out..
It looks like it would work nicely (The weapon pods): the 45 chamfer on the top and that sloped bit at the bottom to clear the big weapon underneath.
<optional> Maybe cut 3 polystyrene tubes for each launcher, seeing those would not look out of place.
THEN the arms looking all huge a beefy makes sense with all that hardware on them and I like it has a bit more flexibility for aiming.
<edit> Maybe add to reinforcement bands over the top of that bare looking gauntlet.
I think for the head, I would slap-on a dome with cut-outs similar to the librarian psychic hood but a smaller opening.
Like a wider Bobba-Fett cut-out to not impede vision when turning the head side-to-side or to look down.
That is a few ideas, I was satisfied with my simple fix in the picture since it addressed the "waddle" issue.
<edit>. I would like some holster for a bolter at the back: the suit looks like it is meant to be an easy-on frame, I think no marine would like to leave his bolter behind.
I also can imagine the frame being a smoking wreck and he pops it off, grabs his bolter and keeps on fighting like nothing happened.