Win Mod12 Trench Gun Conversion

[ssgross]

I still need to add the two dimples or whatever they're called

just thinking out loud - you need a form, and a rounded punch to get it perfect.
https://www.amazon.com/gp/product/B00819DRNE
I bought these when making and attaching clips+rivets to new krag handgaurds.
For a form, you could make your own - drill a hole in a block of hardwood or aluminum, and carefully round over the edge of the hole with a needle file, chamfer tool, whatever works.
Or, maybe a round rivet-set form would work too?
https://www.amazon.com/gp/product/B00QWE5PR6

repro adapter and shield auction now. expensive.
https://www.gunbroker.com/item/942452529