I am assuming that you mean the 1917 U.S. Rifle aka P17. Like MachIV and LoonWulf said, you can set back the barrel assuming that it has not already be done and it should not cost that much.
BTW, if the smith is unfamiliar with 1917 actions, you should strip the bolt of extractor, firing pin, etc. before checking headspace with gages. You use fingertip pressure only as the 1917 has enormous leverage that can allow closing (and damaging) a no-go gage (see Hatcher's Notebook for examples). My suspicion, if you have not been firing hot loads, is that your headspace is fine.
If you have not been noticing hard extraction, short brass life (look for a shiny ring around the brass web), accuracy issues, etc. then it doubles my suspicion that your gunsmith does not know what he is dealing with.
Found another issue doing research--there are two different .280 AI chambers-one with a 30 degree shoulder and one with a 40.
http://www.shootingtimes.com/ammo/ammunition_the_two_chambers_of_the_280_ackley_improved/
Wrong gage gives wrong results.
There are two ways to crosscheck what your smith claims--one is to use cerrosafe for a chamber cast and check the headspace with digital calipers or rent/buy the gages online to check--the problem with the second is if you do not know what the angle is.
The second is to measure the brass before and after using the Hornady headspace comparator for changes in brass size. Use new commercial ammo to do this and I would advise at least substantial eyeprotection. You can also make a homemade headspace gage using Steve Wagner's method (google Steve Wagner gunsmithing or something like that).
Check the headspace yourself before going to the trouble and expense of setting back the barrel. As long as you have not been firing very hot loads that deform the receiver lug recesses (hard extraction etc.) and you can use a dental mirror or cheap borescope to determine this, then my guess is that your rifle is okay. You can also get new old stock bolts for these but these are getting scarce and usually are parkerized WWII replacement bolts. As usual, YMMV.