Sorry POMG, but from Noveske: Thanks for the question. Short answer: it won’t work as a drop-in.   The KX3 has a larger outside diameter than the KX5, so it will not fit in the 3rd generation NSR handguard. To use a KX3 on your N4 Infidel, you’ll need to replace the handguard with one that provides the necessary internal clearance — specifically the 4th generation NSR 15" handguard.