1946 would make it a very early 550-1. The earliest 550s used a bolt with two extractors. It seems that did nothing for reliability, so after WWII it was replaced by a bolt with a single extractor, and the Model 550 (or 550A) was changed to 550-1. From what I can determine, the shell and gas deflector and the grooved receiver top (for a telescopic sight mount) began with 1955 production. The story goes that the reason for the absence of deflectors seen on some later guns is that having the deflector in place makes it more difficult to remove a jammed fired case from the action, so the owner simply removed it. I don't know about that, as I don't remember having a case jam problem with my first 550-1. But I was always careful to clean my rifle after every use, especially the floating chamber (I normally used .22 shorts only). There is crud that can accumulate around the floating chamber and the barrel recess for it after extensive firing of .22 shorts. It's pretty simple to remove and clean the floating chamber as a part of routine cleaning.

BTW - I did order today a pair of 1" ring tip-off mounts (Weaver) off eBay - $10. There are quite a few listed if anyone is interested. I am going to mount a Weaver K4, or possibly an early 2-3/4X Weaver. But the K4 I have is in near-new condition, while the other scope shows more age and wear.