Great question — answering as the UphillTech team:
I have removed similar but square beams using a hatchet and a hammer, with quite a few the split right at the anchor and I was able to remove the anchor with vice grips. There were a few that I had to split several times both horizontally and verticly until I found the anchor. The beams were embedded. Over the tar paper but the metal mesh had been cut I am guessing so they would be tight. We did restucco prior to painting and it looked fine but your slate shake/ cement board will look very nice and you wouldn't need to fill the holes.
Full answer by Ed Beal: https://diy.stackexchange.com/a/154633 (CC BY-SA 4.0).
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