Following up:
I did go ahead and buy the Muzzle-2 Throat-3 rifle. The receiver is a Springfield Armory; serial SA-3767678. May 1945? There's barely any finish left on it, but it's smooth. Sights are functional. There have been some parts replaced; trigger, mag follower, operating rod, etc. The stock is walnut, stamped RA(*)P, it according to the google-foo, it was rebuilt in New Jersey at some point. Couldn't make out the little symbol between the RA and the P. The barrel is dated 4/47.
The receiver is not a re-weld; and if it is, it's a REALLY good one. Machining marks are consistent throughout the op rod channel and a few other places. Drawing number for the receiver is a revision 35; July 44 - October 45 which checks out against the serial number. After doing some reading and checking info on USRifleCAL30M1.com, I went out and stripped it all the way down. Also took the opportunity to take some paint off of the handguard that looked terrible. Barrel looks great; ran a cheap bore scope down it. The windage knob was locked; back the screw out a half-turn and it freed right up.
Pretty neat piece of history in hand. It's gonna see the range tomorrow.
Got a couple hundred rounds of some Prvi Partizan 150gr and 10 en bloc in the mail today.
EDIT: threw some more info at the post. Excited.