I might be able to give you some insight into the chrome bayonet. I have a similar one but with a canvas white slip on cover for the scabbard. It also has a leather foot on the end.
My first duty station was with the Marine Detachment, USS Forrestal CVA-59 from 2/65 to 2/67. Part of our mission was to perform honors and ceremonies for dignitaries. Dress Blues, white duty belts and chrome bayonets. Ours were a bit unusual because they were cut down cadmium plated 03 bayonets from WW1. The were cut down to fit into an M1 scabbard because , as the story goes, a marine brought his rifle up and knocked the cover off the Sec of the Navy.
Mine is dated 1916 with the bursting bomb and SA with the number 23. On the opposite side is a serial number of 635910 with U.S. above the number.
Marine honor guards included these bayonets, in one form or another, for those occasions.
Now if your Grandad was a combat soldier, he may have traded with some other stuff like a NORK bayonet or other field souvenir.
While aboard the Forrestal, I was in charge of the Marine store room. I've traded many things for 'stuff'. Camillis pilots survival knife, flight suit, etc. In fact, my CO, Capt McIlhenny, one day asked me with a smile "Hey Lesnick, are you going to open an Army/Navy Store when you get out"?