Eric - not exactly sure what to call it either. On my Willard 36, construction to hold the SS plate in place was similar with large slot head construction screws lagged into the caprail. The W36s had a channel cut into that stem to lower the anchor down some. Originally, there was a toggle across the top of mine where the forestay for mast was fitted (I had the mast removed).
Here's a picture of my stem fitting area. A heavy U-shaped plate fit into this channel, with the bow roller going across. Old bow roller has bee. Removed and an anchor davit made for a Rocna Vulcan bolted in place.
Here's a link for a socket with screw driver bit. An impact driver might be helpful. God forbid if you strip the head though.
Good luck.
https://www.napaonline.com/en/p/CHQS...70&adtype=pla&