It depends on which rail you use.
If you take a dremel tool or other cutter to your front sight base and cut the bayonet lug and sling swivel off, you have a low profile gas block which should fit under 95% or more of longer rail systems.
I run a LaRue 10" system on a carbine, which has the gas block 7" away from the receiver. No issues, and I can use whatever aftermarket sights I want...