Excellent. I agree that you wouldn't want the lip to be in contact with the tang all the way around the whole edge due to variance, good call there. I was thinking about something that would look a bit like a box-end wrench where it necks down a bit from the circles. Either way, if you've thought about it and considered the options, it's all good.
I have several of the earlier Wardens I could measure pretty accurately as well if you'd like. Just let me know which dimensions you're looking for.