In this picture I made 8 or 10 years ago, you can see I used brass pillars. Don't to that. It makes for dissimilar metals. Don't do stainless either. Some stainless hardens when being cut. Use 1010 steel 3/8" tubing the part number from MSC is in the following drawing.
In this pic you see the relief cut I have made in the rear pillar to clearance for the Timney trigger.
Alternatively, you might bend the sear spring to reduce the pull force on the trigger. That will not get the force as low as the Timney and it will not get you a usable safety, but it will save you $100. There are many videos and posts about how to polish parts in the Mosin Nagant trigger. This is almost all a waste of time. Here is a video where I show how to bend the sear spring and maintain sear to cocking piece engagement.
http://www.youtube.com/watch?v=DPn8IdNJ_SE In this drawing you can see that I made an extra hole in the ATI mount. [for those who can pull off a barrel]
ATI bolt modification kits and ATI stocks may be no good.
But the ATI scope mount for the Mosin Nagant is surprisingly good, and much cheaper than the Rock Solid mount.
Later manufacture ATI mounts have a different coating, and can clear the max dimensions for standard 10-32 cap screws.
You may find ratings for 10-32 screws to take torque from 23 to 68 inch pounds.
Don't do that in this application, and the steel is only .1" thick. I have calculated and verified in .1" thick steel, and back off a 30% safety margin.
Don't go past 20 inch pounds dry or oiled.
Half that with wax on the thread, so don't put wax on the threads.