The Gen 2 lowers have a flared mag well and an integral trigger guard, but otherwise fit all standard AR parts. I also second the suggestion of Vltor uppers for the Gen 2 lowers, as the flared magwell is a good aesthetic match for the squared off Vltor upper.
As far as their normal lowers go, you pay a premium for the roll mark. The vast majority of AR lowers all come from a handful of sources. You can get a lower of the same quality for less, but it won't have the Noveske cross on the side.
As far as lower parts kits go, there are numerous sources for mil-spec kits. The only suggestions I have is maybe look into an after market trigger such as a Geissele or ALG Defense ACT unit.