Parts came from a Lower Parts Kit (LPK) that I happened to have lying around, but if you go to any of the AR parts suppliers you'll find various combinations of parts packaged seperately. As far as the parts fit went, I wanted to use the entire fire control group (trigger, hammer, safety sear, selector) but the slightly 'off' ambi safety that uses the RHS lever to hold things together got in the way. The solution was to turn the lever 180 and screw it back down.There are some issues with small parts fit on the Norcs, mostly springs and detents, but the trigger/hammer/safety sear shouldn't be one. As far as working on an AR lower, you don't even need a good book - if you haven't already, go to AR15 dot com and check out the videos they have posted, I built my first lower on my lunch break with a parts kit, a stripped lower and the videos on ARF. The AR lower is a walk in the park.
PS Questar/ArmsEast/TSE/PD/Wolverine and the vast majority of the sponsors here are terrific sources of both parts and information - just ask when you're ordering and they'll steer you in the right direction