I'm going with a 2 1/2" Model 66 that's been re-barreled.

Not only is the box originally marked as a 2 1/2" barrel, but the product code is for a 2 1/2" barrel.
Also, I can't remember all the 3" serial number prefixes, but I DON'T remember that prefix from that box being used for the 3" range guns.

That's three things that don't match a 3" gun.