What brand and model? Usually the maker has a solution. Got pictures?
Anyway, you wouldn't want a front sight on the receiver rail, the sight radius would be a joke - too short. And you shouldn't mount it on the MOE handguard. What kind of gas block do you have? Railed?
Curious, why didn't you get a standard FSB? They work for most applications.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek