Well, first off, it's either a Remmy or an Eddy, rxvr tells the tale. Bbl should match mfr and date of rxvr.  Get back to me with rxvr mfr and s/n, along with markings near muzzle of bbl, and I can help you with this.
Eddys bring a lower price, ATBE, than Remmys or Winnys.
Just about all parts except springs are stamped with mfr ID letters, either E, R, or W.  Some parts will interchange with P14 Brit rifles, those will be variously marked.
The rifle CAN be restored to "correct" by swapping/buying parts from Numrich.  I've done it.
Unless you are VERY lucky, the front sight will be the incorrect height, as it will probably have been swapped for another during re-build.  Brit Enfield sights will interchange.  I MIGHT be able to help you with this, also.
$400 sounds a little high, but these are becoming scarce, esp in original mil condition.  Sling pictured is incorrect for WWI.
Let me know if I can help.
FWIW, I consider the M1917 to be the BEST mil bolt-action rifle ever made.

If rxvr is Rem, rifle was made sometime prior to Nov 9, 1918.
Aug, 1918 cutoff= 352,199
Sept, 1918   "  = 417,343
Oct, 1918    "  = 475,370
Nov, 1918    "  = 545,541

If rxvr is Eddy, rifle was made prior to May, 1918
Mar, 1918 cutoff= 354,351
Apr, 1918    "  = 422,755
May, 1918    "  = 510,263

Bbl and rxvr mfr should match, and dates should be within a few months of each other.

Original finish on Eddy should be blued (nearly black)  Orig finish on Rem is prob blue, possibly transitioning to parkerized.
www.jouster.com and www.gunandknife.com
Merry Christmas.

"FWIW, I consider the M1917 to be the BEST mil bolt-action rifle ever made."

i agree.

$350-500 is the asking price near me.

i also gotta line on one...a winchester with a $450 price tag. outside, it looks restored...inside, she gauges a little on the worn side. matching as near as i can tell.

Quoted: OK. my bad. It is a Remington. Thanks for all teh info raf. I'll have to get one. Is there a book on these???

Yes, several.

But first, buy the rifle if she "feels good". You know what I mean.  And you, too, Campy.

Brit. Enfield Rifles Vol 4 The Pattern 1914 and U.S. Model 1917 Rifles  by Charles R. Stratton  North Cape Publications ISBN 1-882391-29-2

The Collector's Field Guide Series: Vol Five by J.C. Harison  P-17 The American Enfield  The Arms Chest  ISBN N/A  
Arms Chest
6401 S. Westminster Rd.
Okla. City , OK 73150

The U.S. Enfield  Ian D. Skennerton  Margate, Australia  ISBN 0-949749-02-8

BUY IT.

Merry Christmas.