As said, these are new. So you can pop in any new bolt and 99.999% of the time not worry about the headspace. It's still recommended on the off chance something is out of spec, but I pulled the bolt and carrier assembly out of the M16/SP1 clone I built last year (with about 500rds through it) and used it in my M16A1 upper. I don't have headspace gauges yet, so I fired a single round and inspected the brass (well, steel...it was Wolf), no problems. So I single loaded and fired 4 more rounds. Still no problems. So I single loaded and fired 5 rounds of XM193. Still no problems. I'm satisfied. I'll put a new chrome and notchless bolt/carrier in the other rifle.
And yes, anybodies bolt, carrier and charging handle will fit and function. Last year I bought two of Rock River b/c/ch sets from RBPrecision because they had a sell on them. Go with a quality part and you won't have any problems.