Regarding the question about the third gear lever: Open up this link and turn to page 9 of the manual (Note that it is page 11 of the pdf). There is a paragraph there that explains the third gear lever. Paragraph continues on to page 10.
Regarding the 990 split: Yeah, its easy, but I had to stumble through the first couple of splits I did, as I was unfamiliar with the tractor. I still prefer to remove the fuel tank and the top of the clutch housing. That adds considerable time to the process. Follow the steps in the manual and you will be ok. You should be able to find the manual for free on this website: