Well, click the picture as it's pretty much self-explanatory. I gave the missile bays some missiles and added hatches to the actual bays.
The Rifleman Mech got both arms' weapons cut off and replaced with single barrel guns. I wasn't sure what to do with the stumps of the former lasers, so I added "sensors/lenses". That will at least look better once painted.
The support struts will let the "jeweling" of the cockpit glass (a techniqué that makes the painted glass look like sunlight is reflected in it) look far better.