They aren't necessarily a drop-in fit. Proper clearances have to be established at the right places. The rear handguards are thick and may need to be skimmed down on the inner surface. Front handguards are'nt fully inletted to allow the rear of the handguard line to seat properly. You need to make sure there is adequate clearance for the "tail" of the clip latch and rear face of the firing pin. It's easier to remove wood than to add it though.
Trigger guard lock up can be very tight. Rather than remove wood from the horizontal seats for the trigger housing, you can swap in a used trigger guard with worn locking lugs.