The Diamond Labs frames are available in several styles to suit personal preference such as double trigger versions. The finish is excellent and the quality is top notch. I am a big fan of double triggers. They are comfortable and speed up the trigger pull quite a bit. The Taso Double Trigger is contoured better than the Kingman model and machined of quality metal rather than molded of cheap metal.
Several companies make shark gill type sight rails.
They are all about the same, but the PMI Sight Rail is distinctive - it is sleek, light and graceful. The Lapco vertical adapter provides a stronger and more stable mount for expansion chambers or regulators. It is notched on one side so that once it is installed it will not rotate. This vertical mount is rock solid. Unique Pro Gear Click Velocity Adjuster External velocity adjusters may seem like a good thing, but to be field legal they must be locked down with a set screw.