Forget the shims and bed it right.
Jack Roberts idea of a tapered lug makes a lot of sense. The round receiver doen't have much to resist the torque on the action except at the tang. There should be some clearance under the lug, and a few thousands in front and on the sides, or it will be difficult to get out of the stock with a non-tapered lug. During glass bedding, leaving the masking tape off the front and sides of the lug on the bottom 1/8 in would let the sides and front tighten up at the bottom. It would let you get the action in and out much easier. The tapered lug on the front and sides would be ideal on a round receiver.
On rifles that have flat bottom receivers, the usual masking tape clearance on the sides and front of the lug works well. Any lateral movement of the action in the stock is controlled by bedding the first inch or two of the barrel, under the receiver behind the lug, and the tang area. The flat bottom receiver has a much more surface area to resist any torque than the sides of the recoil lug.