In article , GB wrote:

The simple answer is there aren't any - apart from the skinny (3x2 or so) ceiling joists. Since these are 150 years old, I wouldn't walk on them without care, let alone base any kind of structure on them.

You'll be walking on those when you do the work. Will you support them
temporarily?

He said he was thinking of boards on Acro props. Knowing exactly which bits
are supported from below when working above might be a bit tricky, but at the
least they'll effectively have a much shorter span.