XPOST 1890s 1940s 1990s bath update
Slow progress ... plumber comes later this week to re-install the toilet. But the floor is back to its 1890s materials.
We took advantage of the hole in the floor (under plywood patch in second picture) to have the short run of grey plastic PBE replaced with color-coded PEX. Why that bathroom was plumbed with 4 feet of PEX stubbed off of copper I have no clue. Maybe they ran out of copper? The bath tub and toilet are copper all the way.
Here is a link that might be useful: Original post on old house forum