I finally brought home the rifle and got to look at it more closely.
The rifle displays characteristics of both the early model FBI model 81 ("stacked" model, manufacturer and serial number markings on the receiver, Lyman 41 sight) and the later FBI model 81 (grooves in the barrel jacket, standard rear sight, etc). One theory that I had was that since these are take down rifles, perhaps someone at the FBI had at one time mated a late barrel/forend to an early model receiver and no one had ever corrected it.
Well, scratch that theory...the barrel yoke bears the same serial number as the receiver...

So the mystery continues.
I also noted that the screws on the receiver have been staked. I've not seen that in any other Model 81...even the few FBI model 81's that I've seen
Can anyone identify the numbers stamped on the barrel yoke?
Finally, the barrel code seems to be "NNO". If I'm interpreting this correctly, that would indicate July, of 1944, which seems late for an early FBI model.
