Artificial limbs- you've gained my support!
There should be types of limbs- Articulated and fixed. Fixed are simple to make and can be created in one of few positions: Open(Hauling) Closed(Holding items like picks, spears, swords), "Gripping", etc. Each is better at one task, but worse at the other. So an open hand makes carrying faster, but in combat you can only slap opponents.
Articulated would require more materials, like mechanisms, leather, and the material of choice. Quality of Mechanisms, quality of craftsdwarfship, and the materials (like leather bits, nuts and bolts) determines its speed in adjusting between modes and the suffered penalty of skills( A level 10 swordsdwarf with artificial, well made arm is now level 8[ and capped at 18, not 20] while a level 10 swordsdwarf with a poorly made artificial arm is now level 6 and capped at 16, not 20).
Type of material should also matter. Wood being the cheapest, and lightest alternative, but most fragile. With metals being strong, but heavy. Type of wood or metal also matters, and reflects its armor counterpart( Steel is hard but heavy, copper is somewhat light but weaker in comparison, etc.
For example: A 1000speed dwarf with a wooden arm is 970, as its not hollow, but complete. While a dwarf with 1000 speed and a metal arm is now 900, as again, its complete. The fact if its hollow or full determines its weight, and thus speed reduction, as well as durability, and strength of strikes delivered by it.
There must be disadvantages, or players will amputate their dwarws for benefits of making them as powerful as a colossi.
EDIT: You amputate legs of a dwarf, make them obsidian and now he can wade through 3/7 lava!