Got some more pictures. The patch on the R/H side is well done with a groove cut into the patch and slipped over the matching wedge cut in the stock. The only non matching part(s) are the Tula butt plate and magazine.
When did they transition from the 8 hole piston cover to the 7 hole?
IIRC, they started switching to 7-hole barrel shroud in Jan 1941, but did not complete until Mar/Apr 1941.
Based on your photos: trigger guard is from a later production with full serial stamped during refurb; bolt carrier is from a NKV 314 made SVT; gas cylinder is from a NKV 314 made SVT.
Since it's a Soviet refurb, it is 'naturally' a mixmaster.
BTW, is tip of gas regulator (gas nut) stamped with serial or last 2 digits of the serial?
and is right side of front sight base ep'ed a number?