1. check out the barrel venders listed and supporting this site for your 8 mm chambering
2. See if you can get the owner of the rifle you are interested in to give you the serial ##. Then look it up on this site, That will give you the time it was built and a few other things. Also , it should tell you top / bottom bolt release, and the Mag. type
3." way up there" doesn't tell us where you are located, but the 8 RUM is going to "kill" on both ends , so consider the cost having the barrel threaded for
a break by the Bbl. maker vs having it done by a local gun smith. Feeding the 8 RUM ain't like feeding a 223.