After reading my previous post, I thought I'd share some information, and answers I provided to questions I got from a few members here. This thread is very well alive, and adding more information/pictures is what its all about.
As an alternative to the elusive 40X base, the Redfield/Remington 722 base (cant remember the Redfield part number) looks very similar. It has square corners, and fits newer receivers. The rear section has a 'step' that needs to be cut so the base is the correct length, and a new hole drilled. The Redfield logo and patent ID is stamped on the right side, but that can be ground off.
It is a little thinner than the beefy 40X base, but only an expert would tell. They can be bought on eBay for 10-15$.
Some people asked about the 'green' finish used on the receiver/barrel/base. I have a 700SA base, that was given to me by a buddy who was a 2112 @ Quantico. He's got his feet deep in the USMC as an armorer so I believe pretty much everything he tells me. He gave/sold me most of the stuff I used on my M40, M40A1 and M24 builds.
Apparently, this base came off a retired M40, stashed away and never used. Is it authentic or not? Well, obviously I cant be sure. But we can easily see the 'greenish' tint to the parkerizing, especially the area under the rings when it wasnt affected by the elements/light. It is a very hard finish, finger 'grease' doesnt stain it, its not easily scratched and doesnt reflect light, which was the purpose of the parkerizing.
Now, the buttplate screws. I dont know the exact size/thread, but my guess is that they are standard Remington wood screws. Picture shows the countersink.