I did not know they made a 2 row version. Good to know.
Manure is typically slow-release or converts to useable slowly. I'm surprised there is a response to a later application of it, over applying it pre-plant. Is there any speculation on why it works better applied after the corn is up quite a bit? I could sure learn some more. ;)
Your tractor is plenty of power. It's the floatation. Putting all that weight, if your ground is soft it will really sink in, and a front cultivator you can't lift high enough to get out of the mud.
I'd think cutting down the 56 to a 2 row; or making some 3pt units out of the extra rows would not be too difficult for you. If you get to see a factory model, that will be cool to copy it!