I have one with a Samson Evo 12.7 inch and it look like it would fit under longer hang guard. The adjustment wrenches are also long enough to adjust under the longer tube.
Look at how the gas blocks in the last three links are built!! They are NOT a low profile gas block. The block has to be machined to fit both the gas tube and the adjustment set screw in parallel with each other and still have enough materiel let to make it structurally sound. A set screw from the side is the only way to get a true low profile.
I have two of the Superlative Arms adjustable gas blocks and they fit very well under the forearm, they click adjust from the from front so no set screws are used plus the come with an extra long hex tool to make adjustments with. One on a 25-45 Sharps and the other is on an 264 LBC, both black hole barrels, and they've functioned flawlessly. Hope this helps, also I have other adj low profile gas blocks from other manufactures that require drilling access holes and one that requires the forearm to be removed because the gas adjustment screw faces the reciever. My next two builds I'm going to try the adjustable gas key so I want have to fool with anything forward of the reciever. Good luck on your choice.