And to piggy back what Apilar wrote, before you modify each part, you need to indicate its purpose and function. You need to understand the implications if you can modify too much and its effect on the gun.
Example: For instance, if lets say you found out that the hammer top was catching on the rear of the BBU and you decide to remove some material on the top of the hammer. You run the risk of modifying too much on the hammer that the bbu is unable to push the hammer down during each cycle.
So you need to understand, the function of each part, and its implication on other components when you modify it. You can't throw everything together and expect it to work since a lot of aftermarket parts are not made to spec with their stock counterparts.