I have decided to alter the lightning claw and power fist to better represent the specialized nature of each weapon.
Lightning Claw: melee 2D10+3 Pen 8 Type E Special: Tearing, special
Power fist: 2D10* Pen 12 Type E Special: unbalanced, -2 initiative. The initiative penalty applies regardless of what hand the weapon is placed on and does not stack. This is simply a mechanical means to describe these massive weapons and pull something from the table top.
The power fist is designed to be devastating to armour so I increased the penetration of the weapon to properly illustrate the difference between it and its other melee counterparts. I also altered the balance because I believe that the unwieldy trait was a holdover from DH and added a penalty to initiative because the weapon is powerful but slow. With the application of the DoS melee rule this weapon is clearly the best choice for destroying truely heavy targets.
No doubt there will be more house rules to come in the future as I have not looked at all the heavy weapons.....
The RAW wrist and shoulder mounting seems to be a cut and paste job from the DH rule book because it specifies that it is only effective with pistol type weapons. This makes the upgrade extremely situational in its use, not to mention the fact that there are numerous representations that counter that in the cannon. With that in mind I will allow basic weapon types to use the attachment unless it seems ridiculous.