For a precision rifle the barrel, trigger, and bolt are top consideration. Trigger wise that MBT from LaRue is tops for the money, want something with adjustments and a stellar reputation the Geissele National Match trigger is just outstanding but near 4 times the money. Barrels are the same way, plenty of good button rifled target barrels for reasonable money, Criterion, Ballistic Advantage, Faxon, and many more. I have a BA 20 in. match barrel that shoots great, if you step up to those big name target barrels you can pay three times as much and have a long wait.
Do you want a rifle length buttstock or the carbine length for an adjustable stock? If carbine then get the whole buffer kit from Armalite, it has the correct length extension.
https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201
If rifle length then,
https://www.armalite.com/SACItem.aspx?Item=AR10REKIT02&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201
Barrel length, are you going to push a thousand yards? If not, say 800 yds. and less no reason a 16 in. wouldn't get it done for you. If weight doesnt matter pin that thing down with a 20 in. bull barrel, got my BA 20 inch cheap and like new from someone that just couldn't stand the weight, these things get heavy fast.