There was a post on here titled 3 or 4 inch. It is now 4 pages long and has evolved into a discussion on Lead Bends in older work.
As a older plumber, in my years I have changed many a lead bend. But only one like this. You can see a photo on my web site
www.parrsplumbing.com. There is a page on there titled "More from the Desk of Bill Parr". Clicking on that link will take you to a blog "Plumbing Antiques" The story behind this lead bend is ... you screwed the toilet bowl to the lead bend. That's right a 4" brass thread soldered into the bend. The toilet bowl was made with the male thread as part of the bowl. All you did was grease it up and screw it in. Take a look, please post if you have seen this or know more about it.