If I'm following you correctly, the lug is tight to the bottom of the recoil lug mortise. If that's the case...and the shim you used under the receiver helped the accuracy...that just told you all you need to about clearance under the lug.

I use multiple layers of 10 mil thick vinyl tape on the lugs so it comes out cleanly. This is a pre -64 being done.

Good shootin' -Al

[Linked Image from i.imgur.com]

Forbidden Zoner