1827 Bust Half Overton #?

I agree O-135.

The place to start with attributing Overtons is....Overton. Al's book is one of the few so vital to easy attribution of the issue that even in this electronic age I consider it imperative for Bust Halves. I use a Third Edition acquired used for cheap ($30-ish, if I recall) in conjunction with Heritage Auctions results for the year I'm attributing. A trick when listing Heritage results as an attribution aid - index them with the "list Highest Grade First." The highest-grade examples are the ones which will have careful variety discussion in the auction copy.

That technique works for every issue, and I find it particularly effective when looking into issues I haven't researched much. As regards Overtons, you can add the variety to your original search string for the year and there will likely be enough results for that variety to confirm your thinking one way or the other.