DPMS mags are fine, KAC mags are $$$$$, LaRue mags coming, Magpul mags... someday, never used the c-prod myself, they are stainless which should be nice. I have a bunch of DPMS 19 rounders, never needed more.
Pistol grips: some grips have the big swell which rides the back of the lower receiver on the AR-15; those ones dont work so well on the 308, they leave a gap. I like the Sierra grip myself.
Stocks: if you start with a rifle stock weapon, then you can use all those different rifle stocks, like PRS (as DnPRK mentioned) and Ace ARFX skeleton and so on.
If you start with a factory carbine stocked weapon, you can use all those various stocks: Crane, CTR, MOE, Vltor, etc. The factory carbine stocked guns use an AR-15 tube and come with a stubby buffer. (which is light and should be upgraded) To go from rifle stock to carbine, you just need the right parts.
I did a little writeup on stocks and tubes, might be of interest:
http://www.ar15.com/forums/topic.html?b=3&f=121&t=444682
Handguards are another thing. If you are replacing the barrel nut, then need a DPMS 308 specific one, like from SWS. Some DPMS models use regular carbine handguards, and so you can swap like parts.