As for stocks, if you have the A2 fixed stock version , your stock choices are pretty limited with the A2 buffer tube, but Magpul makes a couple nice choices. If you switch to a carbine buffer and tube, anybody’s adjustable stock will fit. If you already have an adjustable stock, most of the aftermarket adjustable stocks should fit your tube. As mentioned earlier, there are low and high rail uppers. A google search will show you the difference. If you have the high rail, handguard choices are limited, but if you have the low (more common) anyone’s low rail LR308 handguard will work, but you might have to replace the barrel nut to one proprietary to that handguard. It’s a quick job for a gunsmith or someone who has built a lot of AR’s. The Pickatinny slot spacing between the receiver and the handguard might be messed up, preventing you from bridging that gap with a one piece scope mount. But individual scope rings or putting the one piece mount on the receiver fix that.