Value/rarity of 1921/28 Overstamp Thompson

I'm wondering what the value would be on a 95% original finish 21/28 over stamp that is a registered dewat. I'm in the process of getting this piece reactivated and have the original barrel and the welds I know hurt the value but they aren't extremely noticeable. I'm also wondering if anyone has any information pertaining to how many are on the ATF registry. If I have some time I'll post some pics.