Kind of kicking around the idea of cutting up one of my quad rail -M uppers and welding it to a KM stnd. length upper to make a "comp" upper that actually covers a 16" bbl. Obviously, I'd have to machine off the side rails....I'd likely blend/machine/transition to leave like a 3 slot or 5 slot bottom rail for mounting a bipod...then cut KM slots and Durakote or similar the upper.
Just measured it up....looks like adding 4.75" is about perfect. I'd have to machine a channel in the web in that new section of rail to clear a Type 3 buried block.
Hey Nate, if you read this...do you know if the non-accurized Type 2 gas block is interchangeable with a Type 3?