flabigpapa. I am not an expert but I have all of Scott Duff's books. Aug 1940 is the correct date for the receiver. I am looking at the data sheet for a
SA 56745 rifle
date manufactured August 1940
barrel side marking: S-A 8-40 [upside down]
The barrel dates closely followed the receiver dates during that period. Your barrel date does not match the receiver so not likely original. I can see from your photos that the rifle is arsenal rebuilt. The rear handguard clip is wrong, it is sheet metal, should be milled with a groove down the middle. The stock ferrule should also be milled, yours is sheet metal. The stamping on the end of the buttstock is certainly not SA, probably a local arsenal stamp.
The rear sight knobs are not original. A NM operating rod is really not unusual, won't add to the value. Looks like you have a typical arsenal rebuilt rifle, maybe rebuilt a number of times. Seems odd that it has the 10-41 barrel as the ammo was corrosive during WW2. When those rifles were rebuilt, they were disassembled and all the parts were gauged and put in bins. Then on the other end of the plant they were reassembled with the parts taken from those bins at random. So the parts were all mixed up. They paid no attention to manufacturer stamps.
The receiver looks in nice shape. The lower the serial number the more desirable to some. Don't know about value.