Item 27 (Valve Stem) is silver soldered to item 29 (Valve Link Rod)
according to the note on page 14 zone B3 .
But it is not clear to me as to why ... since it is bolted. Maybe for additional mechanical strength.
Additionally there seems to be fit issue with those parts (.087 hole vs .093 pin). Looks like that area needs to be looked into for clarification.
Maybe someone would comment on that.
Instead of Brass for the Piston ... stainless would be the way to go.