As for this scene, I'd say/guess that those are stunt doubles with body armor but that is still a very dangerous stunt (1969) even though you can see the planned safety 'hole' where they are standing. Today, I'd bet that would only be done through CGI.
As for the passing of Mr Goldman, I remember reading "The Princess Bride" (1973) years before the movie (1987) and wondering why there was no movie yet. The movie, when it did come out, was, to me, the BEST adaptation I know of and a wonderful score as well. This is the single instance that I know of where I doff my hat to 'Meathead', Rob Reiner, who directed and coproduced. Perfect casting and Goldman wrote the screenplay as well.