The .22" marking overlapped into 1945 production, so while not particularly common, not really rare either, and I certainly would not give a premium for such a rifle with the receiver marked like that.

Lack of a serial number is an extremely good indication that the rifle was a post-factory assembled rifle. Often, the indicator is that the barrel is not indexed properly. If it is new unfired from the factory, is the SAL tag with the rifle?

The vast majority (I would suggest 99%) of the receivers that are available as replacements were from rifles that were torn down, the serial numbers scrubbed, and the area refinished. Not a lot of care was taken in the scrubbing, so you can usually feel the flat spot where the serial number was. As well, any high macro photo will show the difference between a sanded down area and the pimpling of the original.

For $3995, I would back away. I seriously doubt a new in the box Cno7 with the tags still on it would fetch that much (and I have one of those downstairs).

Not sure I am reading your initial post right: what makes it a number 4?