Thanks, John. I found one of your past posts on the OMNI gearbox.
So, I went and checked out the OMNI website, and it sure looks to be the same product.
I looked at the gearbox yesterday (it's next door at my grandpa's), and 1 number on it was "5A19". There was a second number, much longer though, and didn't bring anything to write it down on.
The part I know is shot is #13 from the diagram<A target="_blank" HREF=http://www.tractorbynet.com/cgi-bin/compact/showflat.pl?Cat=&Board=implement&Number=119702&page=&view=&sb=&o=&vc=1> omni parts breakdown </A>
I am wondering though, what else is missing. My grandpa took the box apart, and left it open, in the rain for about 1 year. It's a bit rusty on the inside, so I wonder if it would be worth fixing.
I'll get some more #'s off the gearbox and cutter this weekend.