Howard,
Use phosphor bronze because the term 'bronze' can include all sorts of unsuitable alloys.
An alternative is to use copper. For example, many people also use larger diameter snap head copper rivets for the side stays. There are plenty of examples on here/ U tube showing rivets being used as stays.
You could also use copper for the bushes but many people talk about machining difficulties with copper. For some reason, I have never had a problem drilling or machining copper – luck maybe???
If in doubt – you could have a chat with your boiler inspector – I'm sure they would help.
Phil H