I found this inside a house we were about to demolish in CLT last Thursday. I can't recall having seen a plane big enough to hold this beast.
That's why I bring my questions here. BTW, there was no plane body to be found, just the iron. I feel like if it had been in a wood body plane there would have been no need for the slot. I'll look closer for markings.
All I know is you gotta make a lotta effort to push that much iron through a piece of wood, even for a thin pass.
Maybe Mark is on the right track. Here's a Cooper's jointer plane for making barrel staves with a 3.5"w blade. The coopers in Williamsburg have them but I haven's seen the details.Just a guess.