Reviving this old thread to add washer specs for anyone who later reads this and needs them.
The small washers to be added for a plastic bottom metal are:
6mm ID x 9mm OD x 1mm
Style# 6807-0609-1000
2 stacked in front, 2 stacked in the back (4 total). They fit snug, and are perfectly flush when installed between the bottom metal and stock (see pic). I had to take a small circular file to the front action screw washers to get the screws to fit flush when installed. That was on 3 separate rifles so it seems to be consistent. Takes 5min. Back screws on all 3 fit with no problem. Plug in the style # on Amazon and there are multiple 60 pack options for about $10. They ship from China.
It took me a little while to measure and locate this correct size so I hope this helps someone else moving forward.
Edit: more pics added.