Wow, that Library of Congress website is a treasure trove of info! I found a ton of good tidbits in just ten minutes of looking through the link provided. I was just about to pay for a copy of the newspaper obit too. Thank you!

What is the approximate birth date for your great-grandfather Michael? Theodore was born in 1863, so I'm estimating John's birthyear as around 1825-1845. I have no information on any of John's siblings, so I can't confirm Michael. Catherine Fisher definitely fits as a name for John's wife, however. We might be on to something here!

@georgetteruth: I noticed the immigration year too, but the records you provided still might help. I have another German ancestor who moved to Wisconsin but traveled back and forth to Germany during his lifetime. He's falsely listed as emigrating several different times because of the ship logs. Theodore still may have emigrated in 1874 but traveled to Germany and back in 1881. Worth a closer look on my part.