You won't have to headspace and time your own barrel - no way. Not on these things. Maybe on your own M2 HB, but not these. SSA may not check headspace, and they were probably trying to get the word out that you need to check your own headspace with the proper gauges. Always to that on a .308 AR build, or have it done for you. Too many variances across this platform to take the chance.
Rainier Arms and Fulton Armory will do that for you, as well as a few other places. Buy your bolt and barrel from the same place, or buy the barrel and send them your bolt. Both of those places will do that; contact them ahead of time if you're sending in your own bolt.
As a general rule, if you use an Armalite-patterned barrel, you have to use the Armalite-patterned bolt. DPMS-patterned barrel, DPMS-patterned bolt.