OK that helps a bit.
You might not even have to do anything if the framing and floor is sound, but because it's old and not typical or common framing for what we would normally do today it wouldn't hurt to add some support.
I would maybe do a couple cement piers w/ 4x4 posts just to be safe.
This is just off the top of my head advice though, really I like to see in person or in pics to be certain(I'm a carpenter/contractor)
Really most of us do not stress on anything under about a 120g, but your situation is not typical.