The receiver with that serial number was put in work during March or April 1936. The Date code on the barrel of KF is K = May, F = 1937. The LK3 is a repair code meaning the gun was back to Ilion for some kind of repair -- L = February, K = 1941. IMP CYL is of course the choke of the barrel. The REP in the oval is Remington's proof mark. I've heard various versions of what the E stands for but most commonly I've heard
Remington
Explosive
Proof. The anchor and the 1 are various inspector's marks.
My 16-gauge Sportsman is also a 26-inch solid rib barrel gun choked improved cylinder but of 1938 vintage, after they had gone to numbering the Sportsman in the same serial number sequence as the Model 11s, so my serial number is 1,521,464 --
with a barrel date code of CG -- C = April, G = 1938.