Quoted:
Ok thats what I was worried about . How is the headspace adjusted from the rear of the bolt or will this cost more than the mosin
I have found that Mosins typically have pretty much interchangable bolt heads. I own a field guage, and I was messing around with a few of my Mosins bolt and none of the several commbinations I tried headspaced incorrectly. I'd just buy a coin type field headspace guage and order a bolt head w/ extractor from online. The guage is inexpensive and chances are that the bolt head you order will work just fine.
ETA: the critical dimensions that determines heaspace on a Mosin is the distance from the rear of the locking lugs on the bolt head to the front of the bolt face, and the distance from the bolt face to the lip of the chamber when the bolt head is locked into place.